The human heart is a muscular organ that pumps blood through the body. It is divided into four chambers - two atria that receive blood and two ventricles that pump blood out. The right side receives deoxygenated blood from the body and pumps it to the lungs. The left side receives oxygenated blood from the lungs and pumps it out to the body through the aorta. Valves control the direction of blood flow between the chambers and vessels. The heart is a vital organ that circulates blood continuously through two circuits - pulmonary circulation to the lungs and systemic circulation to the body.

1. Human Heart
HEART
is a squared
shape, muscular
organ responsible
for pumping blood
through the blood
vessels by
repeated, rhythmic
contractions, or a
similar structure in
annelids,
mollusks, and
arthropods

2. The Heart is divided into two
Right heart
Left heart

3. Right heart
 is a term used to refer collectively to the right atrium and
right ventricle of the heart; occasionally, this term is intended to
reference the right atrium, right ventricle, and the pulmonary trunk
collectively.
The right atrium receives deoxygenated systemic blood from the
superior and inferior vena cavae. The blood is then pumped through
the tricuspid valve into the right ventricle, which in turn pumps the
blood through the pulmonary valve into the pulmonary artery.
Vena cavae, Coronary sinus
→ Right atrium (auricle, fossa ovalis, limbus of fossa
ovalis, crista terminalis, valve of the inferior vena cava,
valve of the coronary sinus)
Tricuspid valve
→ Right ventricle (conus arteriosus, moderator
band/septomarginal trabecula)
Pulmonary valve
→ Pulmonary Artery
→ Pulmonary Circulation

4. Venae cavae
The superior and inferior
vena cava are collectively
called the venae cavae. They are
the veins that return de-
oxygenated blood from the body
into the heart. They both empty
into the right atrium.
The superior vena cava (or
anterior)
 is above the heart, and
forms from a convergence of the
left and right brachiocephalic
veins that contain blood from
the head and the arms. The vena
cavae carry deoxygenated blood
from the body to the right atrium
of the heart.
The venae cavae is the largest
blood vessel in the heart.
The inferior vena cava (or
posterior vena cava)
 travels up alongside the
abdominal aorta with blood from
the lower part of the body.

5. Coronary
Sinus
Coronary Sinus
 is a collection of veins
joined together to form a large
vessel that collects blood from
the myocardium of the heart. It
is present in humans and other
animals.
Location
It is located between the left
atrium and ventricle on the
posterior surface of the heart.
It runs transversely in the
groove between the left atrium
and ventricle on the posterior
surface of the heart.
The coronary sinus orifice
(opening) is just superior to the
septal leaflet of the tricuspid
valve. The coronary sinus orifice
is also known as the ostium of
the coronary sinus

6. Right Atrium
Right Atrium (in older texts
termed the "right auricle")
 is one of four chambers (two
atria and two ventricles) in the
human heart. It receives de-
oxygenated blood from the superior
and inferior vena cavae and the
coronary sinus, and pumps it into
the right ventricle through the
tricuspid valve.
Sinoatrial node (SAN)
 is located within this chamber
next to the vena cava. This is a
group of pacemaker cells which
spontaneously depolarise to create
an Action Potential. The cardiac
action potential then spreads across
both atria causing them to contract
forcing the blood they hold into their
corresponding ventricles.

7. Right Ventricle
Right Auricular Appendix
Fossa Ovalis
Limbus of Fossa Ovalis
Crista Terminalis
Valve of the Inferior Vena Cava
Valve of the Coronary Sinus

8. Right Auricular Appendix
Right auricular
appendix (right auricula,
right auricle) is a small
conical muscular pouch
attached to the right atrium
of the heart. Its margins
present a dentated edge. It
projects from the upper
and front part of the sinus
forward and toward the left
side, overlapping the root
of the aorta.

9. Fossa Ovalis (heart)
Found in the right
atrium of the heart, the
Fossa Ovalis is an
embryonic remnant of
the foramen ovale,
which normally closes
shortly after birth.
Failure of the foramen
ovale to close results
in a disorder known as
patent foramen ovale.

10. Limbus of Fossa Ovalis
Limbus of fossa ovalis
(annulus ovalis)
 is the prominent oval
margin of the fossa ovalis.
It is most distinct above
and at the sides of the fossa;
below, it is deficient.
A small slit-like valvular
opening is occasionally found,
at the upper margin of the fossa,
leading upward beneath the
limbus, into the left atrium; it is
the remains of the fetal aperture
between the two atria.

11. Crista Terminalis
In the development of
the human heart, the right
horn and transverse
portion of the sinus
venosus ultimately
become incorporated with
and form a part of the adult
right atrium, the line of
union between it and the
right auricle being
indicated in the interior of
the atrium by a vertical
crest, the crista terminalis
of His (Wilhelm His, Jr.).

12. Valve of the Inferior Vena
Cava
The valve of the
inferior vena cava
(eustachian valve) serves
to direct the blood from
that vessel through the
foramen ovale into the left
atrium.
The eustachian valve
is the valve at the distal
end of the inferior vena
cava the passes blood
from the lower extremities
into the Right Atrium of the
heart

13. Valve of the Coronary Sinus
The valve of the
coronary sinus (Thebesian
valve) is a semicircular
fold of the lining
membrane of the atrium, at
the orifice of the coronary
sinus. The valve may vary
in size, or be completely
absent.
It may prevent the
regurgitation of blood into
the sinus during the
contraction of the atrium.
This valve may be
double or it may be
cribriform.

14. Tricuspid Valve
Tricuspid valve
 is on the right side of
the heart, between the
right atrium and the right
ventricle. The normal
tricuspid valve usually has
three leaflets and three
papillary muscles.

15. Tricuspid Valve
The largest cusp is interposed between the
atrioventricular orifice and the conus arteriosus and is
termed the anterior or infundibular cusp.
A second, the posterior or marginal cusp, is in relation
to the right margin of the ventricle.
A third, the medial or septal cusp, to the ventricular
septum.
The tricuspid valve prevents the blood from returning
to the right atrium when the right ventricle contracts
***** The tricuspid valve also opens
and closes at periods of time making
the blood flow through from the right
atrium to the right ventricle*****

16. Right Ventricle
Conus Arteriosus
Moderator Band/Septomarginal
Trabecula

17. Right Ventric
le
Right ventricle
 is one of four chambers
(two atria and two
ventricles) in the human
heart. It receives de-
oxygenated blood from the
right atrium via the
tricuspid valve, and pumps
it into the pulmonary artery
via the pulmonary valve.
It is triangular in form,
and extends from the right
atrium to near the apex of
the heart.

18. Conus Arteriosus
Conus Arteriosus
 is a conical pouch formed
from the upper and left angle of
the right ventricle, from which
the pulmonary artery arises.
A tendinous band, which
may be named the tendon of the
conus arteriosus, extends
upward from the right
atrioventricular fibrous ring and
connects the posterior surface
of the conus arteriosus to the
aorta. This is also called the
infundibulum, and it is the
entrance from the right ventricle
into the pulmonary artery and
pulmonary trunk. The wall of the
infundibulum is smooth.

19. Septomargina
l Trabecula
Septomarginal
trabecula (or
moderator band)
 is a muscular band of heart
tissue found in the right ventricle. It
is well-marked in sheep and some
other animals, and frequently
extends from the base of the
anterior papillary muscle to the
ventricular septum.
From its attachments it was
thought to prevent overdistension
of the ventricle, and was named the
"moderator band". However, more
recent research has indicated that it
is more properly considered part of
the electrical conduction system of
the heart, and in that capacity it is
called the "septomarginal
trabecula". The TA name is
"trabecula septomarginalis".
The moderator band is often
used by radiologists to more easily
identify the right ventricle in
prenatal ultrasound.

20. Pulmonary
ValvePulmonary Valve
 is the semilunar valve of the
heart that lies between the right
ventricle and the pulmonary artery
and has three cusps. Similar to the
aortic valve, the pulmonic valve
opens in ventricular systole, when
the pressure in the right ventricle
rises above the pressure in the
pulmonary artery. At the end of
ventricular systole, when the
pressure in the right ventricle falls
rapidly, the pressure in the
pulmonary artery will close the
pulmonic valve.

21. Pulmonary Valve
Pulmonary Artery
Pulmonary Circulation

22. Pulmonary
Artery
Pulmonary arteries carry
blood from the heart to the lungs.
They are the only arteries (other
than umbilical arteries in the
fetus) that carry deoxygenated
blood.
In the human heart, the
pulmonary trunk (pulmonary
artery or main pulmonary artery)
begins at the base of the right
ventricle. It is short and wide -
approximately 5 cm (2 inches) in
length and 3 cm (1.2 inches) in
diameter. It then branches into
two pulmonary arteries (left and
right), which deliver deoxygenated
blood to the corresponding lung.

23. Pulmonary Circulation
Pulmonary Circulation
 is the portion of the cardiovascular system which carries oxygen-
depleted blood away from the heart, to the lungs, and returns oxygenated
blood back to the heart. The term is contrasted with systemic circulation.
Oxygen-depleted blood from the body leaves the right heart through
the pulmonary arteries, which carry it to the lungs, where red blood cells
release carbon dioxide and pick up oxygen during respiration. The
oxygenated blood then leaves the lungs through the pulmonary veins, which
return it to the left heart, completing the pulmonary cycle. The blood is then
distributed to the body through the systemic circulation before returning
again to the pulmonary circulation.

24. Left heart
 is a term used to refer collectively to the left atrium and lef
ventricle of the heart; occasionally, this term is intended to reference
the left atrium, left ventricle, and the aorta collectively.
The left atrium receives oxygenated pulmonic blood from the
pulmonary veins. The blood is then pumped through the mitral valve
into the left ventricle, which in turn pumps the blood through the aortic
valve into the aorta.
The left side of the heart is thicker than the right because of the
requirement to pump blood from the left throughout the body, as
opposed to the right side pumping only through the lungs.
Pulmonary veins
Left atrium
Left Auricular Appendix
Mitral valve
Left ventricle
Aortic valve
Aortic sinus
Aorta
Systemic circulation

25. Pulmonary Veins
The pulmonary veins carry
oxygen-rich blood from the
lungs to the left atrium of the
heart. They are the only veins in
the post-fetal human body that
carry oxygenated (red) blood.
• The pulmonary veins return the
oxygenated blood from the
lungs to the left atrium of the
heart. They are four in number,
two from each lung, and are
destitute of valves. They are
• Right Inferior
• Right Superior
• Left Inferior
• Left Superior

26. Left Atrium
Left atrium
 is one of the four chambers
in the human heart. It receives
oxygenated blood from the
pulmonary veins, and pumps it
into the left ventricle.
Blood is pumped through
the left atrioventricular orifice,
which contains the mitral valve.
A normal left atrium may be up
to 5.5cm in maximum diameter;
any larger than this is a sign of
cardiac failure. This may occur
in cases of mitral regurgitation.

27. Left Auricular Appendix
Left Auricular
Appendix (left
auricula, left
auricle)
 is a conical muscular
pouch connected to the left
atrium of the heart. It is
somewhat constricted at its
junction with the principal
cavity; it is longer, narrower,
and more curved than the right
auricular appendix, and its
margins are more deeply
indented.
It is directed forward and
toward the right and overlaps
the root of the pulmonary artery.

28. Mitral Valve
Mitral valve (also
known as the
bicuspid valve or
left atrioventricular
valve)
 is a dual flap (bi = 2) valve
in the heart that lies between the
left atrium (LA) and the left
ventricle (LV). In Latin, the term
mitral means shaped like a
miter, or bishop's cap. The
mitral valve and the tricuspid
valve are known collectively as
the atrioventricular valves
because they lie between the
atria and the ventricles of the
heart and control flow.

29. Left ventricle
The left ventricle is
one of four chambers
(two atria and two
ventricles) in the human
heart. It receives
oxygenated blood from
the left atrium via the
mitral valve, and pumps
it into the aorta via the
aortic valve.
The left ventricle is
longer and more conical
in shape than the right,
and on transverse
section its concavity
presents an oval or
nearly circular outline. It
forms a small part of the
sternocostal surface and
a considerable part of
the diaphragmatic
surface of the heart; it
also forms the apex of
the heart.

30. Aortic Valve
Aortic valve
 is one of the valves of the
heart. It lies between the left
ventricle and the aorta.
Morphology
The aortic valve has three
cusps. These cusps are half
moon shaped hence also called
aortic semilunar valve. Each
cusp has a small swelling in the
center called the nodule.
Dilatation of the wall of the aorta
behind these cusps is called
aortic sinus. When the aortic
valve is open, the normal size of
the orifice is 3-4 cm² in adults.

31. Aortic Sinus
An aortic sinus is one of the anatomic dilations of the
ascending aorta, which occurs just above the aortic valve.
There are generally three aortic sinuses, the left, the right and the
posterior.
• The left aortic sinus gives rise to the left coronary artery.
• The right aortic sinus gives rise to the right coronary artery.
• Usually, no vessels arise from the posterior aortic sinus, which
is therefore known as the non-coronary sinus.

32. Aorta
The aorta (generally
pronounced [e tə] orɪˈɔː
"ay-orta") is the largest
artery in the human body,
originating from the left
ventricle of the heart and
bringing oxygenated blood
to all parts of the body in
the systemic circulation.
The course of the
Aorta
The aorta is usually divided
into five
segments/sections:
• Ascending aorta
• Arch of aorta
• Descending aorta
• Thoracic aorta
• Abdominal aorta

33. Ascending aorta, Arch of aorta, Descending
aorta
• Ascending Aorta
— the section between the
heart and the arch of aorta
• Arch of Aorta — the
peak part that looks
somewhat like an inverted
"U"
• Descending Aorta
— the section from the
arch of aorta to the point
where it divides into the
common iliac arteries

34. Thoracic aorta
Thoracic aorta
 is contained in the
posterior mediastinal cavity.
It begins at the lower
border of the fourth thoracic
vertebra where it is
continuous with the aortic
arch, and ends in front of the
lower border of the twelfth at
the aortic hiatus in the
diaphragm.
At its commencement, it
is situated on the left of the
vertebral column; it
approaches the median line
as it descends; and, at its
termination, lies directly in
front of the column.

35. Abdominal Aorta
Abdominal Aorta
 is a large artery in
the abdominal cavity.
As part of the aorta, it
is a direct continuation
of descending aorta
(of the thorax).

36. Systemic Circulation
Systemic Circulation
 is the portion of the cardiovascular
system which carries oxygenated
blood away from the heart, to the body,
and returns deoxygenated blood back
to the heart. The term is contrasted
with pulmonary circulation.
Oxygenated blood from the lungs
leaves the left heart through the aorta,
from where it is distributed to the
body's organs and tissues, which
absorb the oxygen, through a complex
network of arteries, arterioles, and
capillaries. The deoxygenated blood is
then collected by venules, from where
it flows first into veins, and then into
the inferior and superior venae cavae,
which return it to the right heart,
completing the systemic cycle. The
blood is then re-oxygenated through
the pulmonary circulation before
returning again to the systemic
circulation.

37. Layers of the Heart
1.) Pericardium
1.1.)Sinus
a.) Oblique Sinus
b.) Transverse Sinus
2.) Epicardium
3.) Myocardium
4.) Endocardium
5.) Cardiac skeleton
5.1.) Fibrous trigone
5.2.) Fibrous rings

38. Pericardium
is a double-walled sac that contains the heart and the roots of the great
vessels.
Layers of Pericardium
A.) Fibrous Pericardium
is the most superficial layer. It is a dense connective tissue,
protecting the heart, anchoring it to the surrounding walls, and
preventing it from overfilling with blood. It is continuous with the outer
adventitial layer of the neighboring great blood vessels.
B.) Serous Pericardium
is deep to the fibrous pericardium. It contains two layers, both of
which function in lubricating the heart to prevent friction from
occurring during heart activity.

39. Pericardial Sinuses
The cul-de-sac enclosed between the limbs of the
inverted U of the venous mesocardium lies behind the left
atrium and is known as the Oblique Sinus.
The passage between the venous and arterial
mesocardia—i.e., between the aorta and pulmonary artery
in front and the atria behind—is termed the Transverse
Sinus.

40. Epicardium
describes the outer layer of heart tissue (from Greek; epi-
outer, cardium heart). When considered as a part of the
pericardium, it is the inner layer, or visceral pericardium.
Its largest constituent is connective tissue and functions as
a protective layer. The visceral pericardium apparently
produces the pericardial fluid, which lubricates motion between
the inner and outer layers of the pericardium.
During ventricular contraction, the wave of depolarization
moves from endocardial to epicardial surface.

41. Myocardium
 is the muscular tissue of the heart.
Relationship to other layers
The other tissues of the heart are:
The Endocardium (inner lining, effectively a specialised endothelium)
The Epicardium (a connective tissue layer around the heart with a
serous surface. It may be considered as the inner (visceral) layer of the
pericardium).
Composition
The myocardium is composed of specialized cardiac muscle cells
with an ability not possessed by muscle tissue elsewhere in the body.
Cardiac muscle, like other muscles, can contract, but it can also
conduct electricity, like nerves.
The blood supply of the myocardium is by the coronary arteries.

42. EndocardiumIn the heart, the endocardium is the innermost layer of tissue that lines
the chambers of the heart. Its cells, embryologically and biologically, are
similar to the endothelial cells that line blood vessels.
The endocardium overlies the much more voluminous myocardium, the
muscular tissue responsible for the contraction of the heart. The outer layer
of the heart is termed epicardium and the heart is surrounded by a small
amount of fluid enclosed by a fibrous sac called the pericardium.
Function
Recently, it has become evident that the endocardium, which is
primarily made up of endothelial cells, controls myocardial function. This
modulating role is separate from the homeometric and heterometric
regulatory mechanisms that control myocardial contractility. Moreover, the
endothelium of the myocardial (heart muscle) capillaries, which is also
closely appositioned to the cardiomyocytes (heart muscle cells) are involved
in this modulatory role. Thus, the cardiac endothelium (both the endocardial
endothelium and the endothelium of the myocardial capillaries) controls the
development of the heart in the embryo as well as in the adult, for example
during hypertrophy. Additionally, the contractility and electrophysiological
environment of the cardiomyocyte are regulated by the cardiac endothelium.
The endocardial endothelium may also act as a kind of blood-heart
barrier (analogous to the blood-brain barrier), thus controlling the ionic
composition of the extracellular fluid in which the cardiomyocytes bathe.

43. Cardiac skeleton
Cardiac skeleton (sometimes called "fibrous skeleton of the heart") refers to
the structure of dense connective tissue in the heart that separates the atria
from the ventricles.
It is not a "true" skeleton, but it does provide structure and support for
the heart, as well as isolating the electric charges that go through the heart.
The left atrioventricular ring is closely connected, by its right margin,
with the aortic arterial ring; between these and the right atrioventricular ring
is a triangular mass of fibrous tissue, the fibrous trigone, which represents
the os cordis seen in the heart of some of the larger animals, as the ox and
elephant.
The right and left fibrous rings of heart (anulus fibrosus cordis)
surround the atrioventricular and arterial orifices, and are stronger upon the
left than on the right side of the heart. The right fibrous ring is known as the
anulus fibrosus dexter cordis, and the left is known as the anulus fibrosus
sinister cordis

44. Heart Structures
A.) Atria
*Interatrial septum
*Musculi pectinati
B.) Ventricle
*Interventricular Septum
*Trabeculae Carneae
*Chordae Tendinae
*Papillary Muscle
C.) Valve
1.) Atrioventricular valves
1.1.) Mitral valve
1.2.) Tricuspid valve
2.) Semilunar valves
2.1.) Aortic valve
2.2.) Pulmonic valve

45. Interatrial septum
Interatrial Septum is the wall of tissue that separates the
right and left atria of the heart.

46. Musculi Pectinati
In the right atrium,
behind the crest the
internal surface of the
atrium is smooth, while in
front of it the muscular
fibers of the wall are
raised into parallel ridges
resembling the teeth of a
comb, and hence named
the musculi pectinati
(pectinate muscles).

47. Interventricular
Septum

48. Interventricular Septu
m
Interventricular septum (or
ventricular septum, or during
development septum inferius) is
the stout wall separating the lower
chambers (the ventricles) of the
heart from one another.
The ventricular septum is
directed obliquely backward and to
the right, and is curved with the
convexity toward the right ventricle:
its margins correspond with the
anterior and posterior longitudinal
sulci.
Portions
The greater portion of it is
thick and muscular and constitutes
the muscular ventricular septum.
Its upper and posterior part,
which separates the aortic
vestibule from the lower part of the
right atrium and upper part of the
right ventricle, is thin and fibrous,
and is termed the membranous
ventricular septum (septum
membranaceum).

49. Trabeculae Carneae
The trabeculae carneae (columnae carneae) are rounded
or irregular muscular columns which project from the whole of
the inner surface of the ventricle, with the exception of the
conus arteriosus.
They are of three kinds:
1.) Some are attached along their entire length on one side and merely
form prominent ridges,
2.) Others are fixed at their extremities but free in the middle,
3.) While a third set (musculi papillares) are continuous by their bases with
the wall of the ventricle, while their apices give origin to the chordæ
tendineæ which pass to be attached to the segments of the tricuspid valve.

50. Chordae Tendinae
The chordae
tendineae, or heart
strings, are cord-like
tendons that connect the
papillary muscles to the
tricuspid valve and the
mitral valve in the heart.
When the right
ventricle of the heart
contracts, the blood
pressure pushes the
tricuspid valve which closes
and prevents a backflow of
blood into the right atrium.
The chordae tendineae
prevents the flaps from
being everted into the right
atrium. Similarly, these
cord-like tendons hold in
position other flaps like the
bicuspid or mitral valve.

51. Papillary Muscle
Papillary muscles of
the heart serve to limit
the movements of the
mitral and tricuspid
valves. These muscles
contract to tighten the
chordae tendineae,
which in turn prevent
inversion. This occurs
in response to
pressure gradients.
Instead they brace the
valves against the high
pressure, preventing
regurgitation of
ventricular blood back
into the atrial cavities.

52. Heart Valves
Heart valves are
valves in the heart that
maintain the
unidirectional flow of
blood by opening and
closing depending on
the difference in
pressure on each side.
The mechanical
equivalent of the heart
valves would be the
reed valves.

53. Mitral Valve
The mitral valve
(also known as the
bicuspid valve or left
atrioventricular valve), is
a dual flap (bi = 2) valve in
the heart that lies between
the left atrium (LA) and the
left ventricle (LV). In Latin,
the term mitral means
shaped like a miter, or
bishop's cap. The mitral
valve and the tricuspid
valve are known
collectively as the
atrioventricular valves
because they lie between
the atria and the ventricles
of the heart and control
flow.

54. Tricuspid Valve
The tricuspid valve
is on the right side of the
heart, between the right
atrium and the right
ventricle. The normal
tricuspid valve usually has
three leaflets and three
papillary muscles.
Tricuspid valves may also
occur with two or four
leaflets, and the number
may change during life.

55. Aortic Valve

56. Aortic Valve
The aortic valve is one of the valves of the heart. It lies between the
left ventricle and the aorta.
Morphology
The aortic valve has three cusps. These cusps are half moon shaped
hence also called aortic semilunar valve. Each cusp has a small swelling in
the center called the nodule. Dilatation of the wall of the aorta behind these
cusps is called aortic sinus. When the aortic valve is open, the normal size
of the orifice is 3-4 cm² in adults.
Function & Physiology
During ventricular systole, pressure rises in the left ventricle. When the
pressure in the left ventricle rises above the pressure in the aorta, the aortic
valve opens, allowing blood to exit the left ventricle into the aorta. When
ventricular systole ends, pressure in the left ventricle rapidly drops. When
the pressure in the left ventricle decreases, the aortic pressure forces the
aortic valve to close. The closure of the aortic valve contributes the A2
component of the second heart sound (S2).

57. Pumonary Valve

58. Pumonary Valve
is the semilunar valve of the heart that lies between the
right ventricle and the pulmonary artery and has three
cusps. Similar to the aortic valve, the pulmonic valve
opens in ventricular systole, when the pressure in the right
ventricle rises above the pressure in the pulmonary artery.
At the end of ventricular systole, when the pressure in the
right ventricle falls rapidly, the pressure in the pulmonary
artery will close the pulmonic valve.
The closure of the pulmonic valve contributes the P2
component of the second heart sound (S2). The right heart
is a low-pressure system, so the P2 component of the
second heart sound is usually softer than the A2
component of the second heart sound. However, it is
physiologically normal in some young people to hear both
components separated during inhalation.

59. Regions of The Heart
1.) Base
2.) Apex
3.) Grooves
a.) Coronary/atrioventricular
b.) Interatrial
c.) Anterior interventricula
d.) Posterior interventricular
4.) Surfaces
a.) Sternocostal
b.) Diaphragmatic
5.) Borders
a.) Right
b.) Left

60. Base of the Heart
Base of the heart, directed upward, backward,
and to the right, is separated from the fifth,
sixth, seventh, and eighth thoracic vertebræ
by the esophagus, aorta, and thoracic duct.
It is formed mainly by the left atrium, and,
to a small extent, by the back part of the right
atrium.
Somewhat quadrilateral in form, it is in
relation above with the bifurcation of the
pulmonary artery, and is bounded below by
the posterior part of the coronary sulcus,
containing the coronary sinus.
On the right it is limited by the sulcus
terminalis of the right atrium, and on the left by
the ligament of the left vena cava and the
oblique vein of the left atrium.
The four pulmonary veins, two on either
side, open into the left atrium, while the
superior vena cava opens into the upper, and
the anterior vena cava into the lower, part of
the right atrium.

61. Apex of the
Heart
Apex of the heart
 is the lowest superficial part of
the heart.
It is directed downward, forward,
and to the left, and is overlapped by
the left lung and pleura.
External Anatomy
It lies behind the fifth left
intercostal space, 8 to 9 cm. from the
mid-sternal line, slightly medial to the
midclavicular line.
Alternately, it can be found about
4 cm. below and 2 mm. to the medial
side of the left mammary papilla.
It's function is to pump blood to
left atruim

62. Grooves
Coronary/atrioventricular
Interatrial
Anterior interventricula
Posterior interventricular

63. Coronary Sulcus
The atria of the heart are separated from
the ventricles by the coronary sulcus
(coronary groove, auriculoventricular
groove, atrioventricular groove); this
contains the trunks of the nutrient vessels
of the heart, and is deficient in front, where
it is crossed by the root of the pulmonary
artery.

64. Interatrial Groove
Interatrial groove, separating the
two atria, is scarcely marked on the
posterior surface, while anteriorly it is
hidden by the pulmonary artery and
aorta.

65. Anterior Interventricular
Sulcus
The ventricles of the heart are separated
by two grooves, one of which, the anterior
longitudinal sulcus (or anterior
interventricular sulcus), is situated on the
sternocostal surface of the heart, close to its
left margin. The other groove separating the
ventricles is the posterior interventricular
sulcus.

66. Posterior Interventricular
Sulcus
The ventricles are separated by two grooves,
one of which, the anterior longitudinal sulcus, is
situated on the sternocostal surface of the heart,
close to its left margin, the other posterior
longitudinal sulcus (posterior interventricular
sulcus, inferior interventricular groove), on the
diaphragmatic surface near the right margin.
In it run the posterior interventricular artery
and middle cardiac vein.

67. Surfaces
Sternocostal
Diaphragmatic

68. Sternocostal Surface of
Heart
The sternocostal surface of the heart (anterior
surface of the heart) is directed forward, upward,
and to the left.
Its lower part is convex, formed chiefly by the
right ventricle, and traversed near its left margin
by the anterior longitudinal sulcus.
Its upper part is separated from the lower by
the coronary sulcus, and is formed by the atria; it
presents a deep concavity, occupied by the
ascending aorta and the pulmonary artery.

69. Diaphragmatic Surface of
Heart
The diaphragmatic surface of the heart,
directed downward and slightly backward,
is formed by the ventricles, and rests upon
the central tendon and a small part of the
left muscular portion of the diaphragm.
It is separated from the base by the
posterior part of the coronary sulcus, and is
traversed obliquely by the posterior
longitudinal sulcus.

70. Borders
Right Border of Heart
Left Margin of Heart

71. Right Border of Heart
Right margin of the heart (right border
of heart)
 is long, and is formed by the right atrium above and the
right ventricle below.
The atrial portion is rounded and almost vertical; it is
situated behind the third, fourth, and fifth right costal
cartilages about 1.25 cm. from the margin of the sternum.
The ventricular portion, thin and sharp, is named the
acute margin; it is nearly horizontal, and extends from the
sternal end of the sixth right coastal cartilage to the apex
of the heart.

72. Left Margin of Heart
The left margin of heart (or obtuse margin) is shorter
than the right border of heart, full, and rounded: it
is formed mainly by the left ventricle, but to a
slight extent, above, by the left atrium.
It extends from a point in the second left
intercostal space, about 2.5 mm. from the sternal
margin, obliquely downward, with a convexity to
the left, to the apex of the heart.

73. Electrical conduction
system of the heart
The normal electrical conduction in the heart allows the
impulse that is generated by the sinoatrial node (SA node)
of the heart to be propagated to (and stimulate) the
myocardium (Cardiac muscle). After myocardium is
stimulated, it contracts. It is the ordered stimulation of the
myocardium that allows efficient contraction of the heart,
thereby allowing blood to be pumped throughout the body.
Cardiac Pacemaker
SA node
AV node
Bundle of His
Purkinje Fibers

74. Cardiac Pacemaker
The contractions of the heart are controlled by
chemical impulses, which fire at a rate which controls the
beat of the heart.
The cells that create these rhythmical impulses are
called pacemaker cells, and they directly control the heart
rate. Artificial devices also called pacemakers can be
used after damage to the body's intrinsic conduction
system to produce these impulses synthetically.

75. Sinoatrial node
Sinoatrial node (abbreviated SA
node or SAN, also called the sinus
node)
 is the impulse generating (pacemaker) tissue
located in the right atrium of the heart. It is a group
of cells positioned on the wall of the right atrium,
near the entrance of the superior vena cava. These
cells are modified cardiac myocytes. They possess
some contractile filaments, though they do not
contract.

76. Atrioventricular node
Atrioventricular node (abbreviated
AV node)
 is an area of specialized tissue between the atria
and the ventricles of the heart, which conducts the
normal electrical impulse from the atria to the
ventricles. The AV node is also known as the
Aschoff-Tawara node.
The AV node receives two inputs from the atria:
posteriorly via the crista terminalis, and anteriorly
via the interatrial septum.
An important property that is unique to the AV
node is decremental conduction. This is the property
of the AV node that prevents rapid conduction to the
ventricle in cases of rapid atrial rhythms, such as
atrial fibrillation or atrial flutter.

77. Bundle of His
Bundle of His
 is a collection of heart
muscle cells specialized for
electrical conduction that
transmits the electrical impulses
from the AV node (located
between the atria and the
ventricles) to the point of the
apex of the fascicular branches.
The fascicular branches then
lead to the Purkinje fibers which
innervate the ventricles, causing
the cardiac muscle of the
ventricles to contract at a paced
interval. These specialized
muscle fibres in the heart were
named after the Swiss
cardiologist Wilhelm His, Jr.,
who discovered them in 1893.

78. Purkinje Fibers
Purkinje fibers (or Purkyne tissue) are located in the
inner ventricular walls of the heart, just beneath the
endocardium. These fibers are specialized myocardial
fibers that conduct an electrical stimulus or impulse that
enables the heart to contract in a coordinated fashion.
Function
Purkinje fibers work with the sinoatrial node (SA node)
and the atrioventricular node (AV node) to control the heart
rate.
During the ventricular contraction portion of the
cardiac cycle, the Purkinje fibers carry the contraction
impulse from the left and right bundle branches to the
myocardium of the ventricles. This causes the muscle
tissue of the ventricles to contract and force blood out of
the heart — either to the pulmonary circulation (from the
right ventricle) or to the systemic circulation (from the left
ventricle).