The human heart is a muscular organ located in the chest between the lungs. It has a mass of 250-350 grams and size of a fist. The heart is divided into four chambers - two upper atria and two lower ventricles. It pumps blood continuously through the circulatory system to provide blood flow throughout the body. During each cardiac cycle, the heart contracts (systole) to pump blood out and relaxes (diastole) to allow blood to fill the chambers. There are two main audible heart sounds, S1 and S2, which correspond to the closing of the atrioventricular and semilunar valves.

1. HUMAN HEART
The heart is a muscular organ that functions as a pump in
the circulatory system to provide a continuous flow of blood
throughout the body.
PositionandsizeofHumanHeart
 In humans, the heart is located between the lungs, in the middle
compartment of the chest
 It is felt to be on the left because the left heart is stronger and
larger, since it pumps blood to all the body parts.

2.  mass of 250–350 grams and size of a fist.
Structure
Right atrium. Left atrium
Left Ventricle
Right Ventricle
NumberofChambers
 In homeothermic animals, i.e. mammals, and birds, the heart is
divided into four chambers: upper left and right atria; and lower
left and right ventricles.
 In poikilothermic organisms, like Fish has two chambered heart
while amphibians and reptiles have 3 chambered heart. It causes
the mixing of oxygenated and deoxygenated blood.

3. Fish( 2- Chambered) Frog(3-Chambered) Reptile(3-Chambered)
Valves

4.  Valve between
the right atrium
and the right
ventricle is
the tricuspid
valve.
 The mitral
valve lies
between the left
atrium and left
ventricle. It is
also known as
the bicuspid
valve.
 The papillary
muscles extend
from the walls of
the heart to
valves by
cartilaginous
connections
called chordae
tendineae. These
muscles prevent the valves from falling too far back when they
close.
 Two additional semilunar valves :
 Pulmonary valve is located at the base of the pulmonary
artery
 semilunar aortic valve is at the base of the aorta
These valves have pocket like structure which gets filled with
back flow of blood in pulmonary artery and aorta, when
ventricles relax, thus sealing the valves.

5. BloodVessels
Pulmonary Artery Pulmonary Vein
Superior and inferior. Aorta
Vena cava
FunctioningofHeart

6. Cardiac cycle refers to the sequence of mechanical and electrical
events that repeats with every heartbeat. It lasts approximately 0.8
seconds.
Cardiac muscle tissue has auto rhythmicity, the unique ability to
initiate cardiac action potential.

7. PhasesoftheCardiacCycle Heart rhythmically
contracts( systole ) and relaxes( diastole)
1. JOINT DIASTOLE
2. ATRIAL SYSTOLE AND VENTRICULAR DIASTOLE
3. VENTRICULAR SYSTOLE
4. VENTRICULAR DIASTOLE
Heart sounds—- lub dub
In a normal, healthy heart, there are only two audible heart sounds:
1. S1 is the sound created by the closing of the atrioventricular valves during
ventricular contraction and is normally described as a “lub,” or first heart
sound.
2. The second heart sound, S2, is the sound of the closing of the semilunar
valves during ventricular diastole and is described as a “dub”.