The cardiac cycle describes the sequence of events in one heartbeat. It begins with spontaneous generation of an action potential in the sinus node which then spreads to the atria and ventricles. Each cycle consists of a diastolic phase where the heart relaxes and fills with blood, followed by a systolic phase where the heart contracts and pumps blood out. Key events include atrial systole, isovolumetric contraction, ventricular ejection, reduced ejection, isovolumetric relaxation, and rapid ventricular filling. The cycle repeats with each heartbeat to circulate blood through the body.

1. CARDIAC CYCLE

2. OBJECTIVES

1.Enumerate the phases of cardiac cycle
2.Explain the effect of heart rate on duration of systole and
diastole
3.Recognize the pressure, electrical, sound and volume
changes during cardiac cycle
4.Correlate different phases of cardiac cycle with various
changes in events
5.Compare and contrast left and right ventricular pressures
and volumes during the normal cardiac cycle
6.Describe atrial pressure waves & their relationship to
cardiac cycle
7.Describe the use of the pressure-volume loop in
describing the phases of the cardiac cycle

3. FACTS ABOUT OUR HEART
 Pumping is the main function of the heart.
● It is the size of a fist and weighs about 250 grams

● In a lifetime, it beats 3 billion times and pumps 110 million gallons of
blood (2000 gallons/day.)

● Every day, your heart creates enough energy to drive a truck for 20
miles (32 km.) In a lifetime, that is equivalent to driving to the moon and
back.

● Our heart has its own electrical impulse, it can continue to beat even
when separated from the body, as long as it has an adequate supply of
oxygen.

● Heart is a double pump (right & left) that work together

● It has two circulations: systemic & pulmonary circulation which

9. CARDIAC CYCLE
 Describing the sequence of events in one
heart beat

10.  Cardiac events that occur from the
beginning of one heart beat to the
beginning of the next is called C Cycle.
 TIME OF ONE CYCLE : O.8 SECONDS
 So, 75 beats x 0.8 = 60 seconds or 1
mnt.
 MECHANICAL & ELECTRICAL
EVENTS
 DIASTOLE SYSTOLE

13. CARDIAC CYCLE
The cardiac events that occur from the beginning of one heartbeat to
the beginning of the next are called the cardiac cycle.
Each cycle is initiated by spontaneous generation of an action
potential in the sinus node.
AP → Atria → A – V bundles → Ventricles.
AV Delay - .1 sec
Diastole: Period of relaxation – heart fills with blood.
Systole: Period of contraction – heart pumps the blood.

14. CARDIAC CYCLE
 Contraction of the myocardium generates pressure
changes which result in the orderly movement of blood.
 Blood flows from an area of high pressure to an area
of low pressure, unless flow is blocked by a valve.
 Events on the right and left sides of the heart are the
same, but pressures are lower on the right.

15. Diastole
systole
Blood ejected to aorta and
pulmonary trunk
Blood comes to ventricles through
AV valve from atria

16.  Valves open passively & close actively due to
pressure gradients
 AV valves open when P in atria > P in ventricles
 AV valves close when P in ventricles > P in atria
 Semilunar valves open when P in ventricles > P in
arteries
 Semilunar valves close when P in arteries > P in
ventricles

17. CARDIAC CYCLE
Normal average HR 75 bpm. Duration of each cardiac cycle is
60/75=0.8 sec
Atrial cycle:
1. Atrial systole – 0.1 sec
2. Atrial diastole – 0.7 sec
Ventricular cycle:
Ventricular systole (0.3 sec)
1. Isovolumic contraction – 0.05 sec
2. Ventricular ejection: rapid ejection – 0.1 sec, slow ejection – 0.15 sec
Ventricular diastole (0.5 sec)
1. Protodiastole - 0.04 sec
2. Isovolumic relaxation – 0.06 sec
3. Rapid passive filling – 0.11 sec
4. Reduced filling (diastasis) – 0.19 sec
5. Last rapid filling – 0.1 sec

24. ATRIAL SYSTOLE
THE END OF DIASTOLE

25. ATRIAL SYSTOLE - HEART
 Prior to atrial systole, blood has
been flowing passively from the
atrium into the ventricle through
the open AV valve.
 Contraction of atria propels some
additional blood into the
ventricles. Atrial contraction is
complete before the ventricle
begins to contract.

30. ATRIAL SYSTOLE
PRESSURES & VOLUMES
 The "a" wave occurs when the
atrium contracts, increasing atrial
pressure (yellow).
 Blood arriving at the heart cannot
enter the atrium so it flows back up
the jugular vein, causing the first
discernible wave in the jugular
venous pulse.
 Atrial pressure drops when the atria
stop contracting.

31. ATRIAL SYSTOLE
1
Function of Atria as primer pumps :
80 % of Blood directly flows in
20 % of blood by Atrial Contraction
ATRIAL PRESSURE ELEVATION WAVE
a – wave c – wave v – wave
a – wave = atrial contraction and the
Pressure from 4 -6 goes up to 7-8 mmH
c- wave = ventricular contraction
bulging of AV Valves.
v – wave = end of ventricular contractio
flow blood from veins to atria.

32. ISOVOLUMETRIC CONTRACTION
The Beginning of systole

33. VENTRICULAR SYSTOLE
Isovolumic contraction: Immediately after ventricular contraction
begins, the ventricular pressure rises abruptly, causing the A-V
valves to close.
An additional 0.02 to 0.03 second is required for the ventricle to
build up sufficient pressure to push the semilunar valves open
against the pressures in the aorta and pulmonary artery.
Therefore, during this period, contraction is occurring in the
ventricles, but there is no emptying. This is called the period of
isovolumic or isometric contraction, meaning that tension is
increasing in the muscle but little or no shortening of the muscle
fibers is occurring.

38. 2
ISOVOLUMETRIC
VENTRICULAR CONTRACTION
ISOVOLUMIC + ISOMETRIC =
ISOVOLUMETRIC
 Ventricular pressure rises abruptly causing
AV VALVES closes.
 Then additional 0.02 -0.03 seconds
Required for the ventricle to build
Sufficient pressure to push aortic , pulmo.
Valves.
 Therefore this period is called Iso Vol.
contraction meaning –tension is building
up with no shortening of muscle

39. VENTRICULAR SYSTOLE
Ventricular Ejection: When the left ventricular pressure
rises slightly above 80 mm Hg and the right ventricular
pressure slightly above 8 mm Hg, the ventricular pressures
push the semilunar valves open.
Immediately, blood begins to pour out of the ventricles,
with about 70 per cent of the blood emptying occurring
during the first third of the period of ejection - and the
period of rapid ejection.
Remaining 30 per cent emptying during the next two
thirds – the period of slow ejection.

40. 3
Ventricular pressure raises above
to 8
and 80 mm Hg in RV & LV .
PERIOD OF RAPID EJECTION
PERIOD OF SLOW EJECTION
VENTRICULAR EJECTION
FIRST -- RAPID 1/3 - 70 %
SECOND – SLOW 2/3 - 30 %

45. REDUCED EJECTION
THE END OF SYSTOLE

46. REDUCED EJECTION
HEART
 At the end of this phase the
semilunar (aortic and pulmonary)
valves close.

50. REDUCED EJECTION
PRESSURES & VOLUMES
 After the peak in ventricular and arterial
pressures (red and green), blood flow
out of the ventricles decreases and
ventricular volume decreases more
slowly (white).
 When the pressure in the ventricles falls
below the pressure in the arteries, blood
in the arteries begins to flow back
toward the ventricles and causes the
semilunar valves to close. This marks
the end of ventricular systole
mechanically.

52. VENTRICULAR DIASTOLE
Protodiastole: Once the ventricular muscle is fully contracted, the already falling
ventricular pressures drop more rapidly.
The elevated pressures in the distended large arteries that have just been filled
with blood from the contracted ventricles immediately push blood back toward the
ventricles, which snaps the aortic and pulmonary valves closed. (second heart
sound)
Isovolumic relaxation: At the end of systole, ventricular relaxation begins
suddenly, allowing both the right and left intraventricular pressures to decrease
rapidly.
For another 0.03 to 0.06 second, the ventricular muscle continues to relax, even
though the ventricular volume does not change, giving rise to the period of
isovolumic or isometric relaxation.
During this period, the intraventricular pressures decrease rapidly back to their
low diastolic levels. Then the A-V valves open to begin a new cycle of ventricular
pumping.

53. ISOVOLUMETRIC RELAXATION
THE BEGINNING OF DIASTOLE

54. ISOVOLUMETRIC RELAXATION
HEART
 At the beginning of this phase the
AV valves are closed.

56. 4
ISOVOLUMETRIC
VENTRICULAR RELAXATION
DIASTOLE
Intra ventricular pressure drops at the e
Of the ventricular systole. Aorta, Pulm.
Artery snaps back blood and Aortic,
pulmonary valves closes .
For about 0.03 to 0.06 seconds
ventricular muscle relaxes even thoug
ventricular volume does not change
giving rise to Isovolumetric relaxation.

59.  During this period intra ventricular pressure
decreases rapidly back to their low diastolic
levels.
 Then the AV Valves open to begin a new
cycle of Ventricular pumping.

61. ISOVOLUMETRIC RELAXATION
PRESSURES & VOLUMES
 Throughout this and the previous
two phases, the atrium in diastole
has been filling with blood on top
of the closed AV valve, causing
atrial pressure to rise gradually
(yellow).
 The "v" wave is due to the back
flow of blood after it hits the
closed AV valve. It is the second
discernible wave of the jugular
venous pulse.
 The pressure in the ventricles
(red) continues to drop.
 Ventricular volume (white) is at a
minimum and is ready to be filled
again with blood.

62. RAPID VENTRICULAR FILLING
HEART
 Once the AV valves open, blood
that has accumulated in the atria
flows rapidly into the ventricles.

66. RAPID VENTRICULAR FILLING PRESSURES &
VOLUMES
 Ventricular volume (white)
increases rapidly as blood flows
from the atria into the ventricles.

70. Ventricular volume (white) increases more
slowly now. The ventricles continue to fill
with blood until they are nearly full.

71. VENTRICULAR DIASTOLE
Rapid passive filling: During ventricular systole, large amounts of blood
accumulate in the right and left atria because of the closed A-V valves.
Therefore, as soon as systole is over and the ventricular pressures fall
again, the moderately increased pressures that have developed in the atria
during ventricular systole immediately push the A-V valves open and allow
blood to flow rapidly into the ventricles - the rise of the left ventricular
volume curve. (70% approx.)
Reduced filling (diastasis): During the middle third of diastole, only a
small amount of blood normally flows into the ventricles that continues to
empty into the atria from the veins and passes through the atria directly
into the ventricles. (20% approx.)
Last rapid filling: During the last third of diastole, the atria contract and
give an additional thrust to the inflow of blood into the ventricles; this
accounts for about 10 per cent of the filling of the ventricles. (10% approx.
- atrial kick)

90. LENGTH
 Cardiac muscle has the unique property of contracting and repolarizing faster
when the heart rate is high and the duration of systole decreases from 0.3 s at a
heart rate of 65 to 0.16 s at a rate of 200 beats/min.
 The duration of systole is much more fixed than that of diastole, and when the
heart rate is increased, diastole is shortened to a much greater degree.
 This fact has important physiologic and clinical implications. It is during
diastole that the heart muscle rests, and coronary blood flow to the
subendocardial portions of the left ventricle occurs only during diastole.
 Most of the ventricular filling occurs in diastole. At heart rates up to about 180,
filling is adequate as long as there is sufficient venous return, and cardiac
output per minute is increased by an increase in rate.
 However, at very high heart rates, filling may be compromised to such a degree
that cardiac output per minute falls and symptoms of heart failure develop.

91. LEFT VENTRICULAR
PRESSURE/VOLUME P/V LOOP
LEFT
VENTRICULAR
PRESSURE
(mmHg)
LEFT VENTRICULAR VOLUME (ml)
A B
C
D
E
F
100 150
50
0
120
40
80

93. 2） Pressure changes in the atria, the a, c, and v waves.
 a wave, the atrial
contraction
 c wave, bulging of the
A-V valves when the
ventricles begin to
contract

94.  v wave, at the end of ventricle contraction,
 caused by the accumulated blood in the atria
while the A-V valves are closed

95. The sounds heard over the cardiac
region produced by the functioning of
the heart.
Heart Sounds

96. HEART SOUNDS
 S1- first sound
 Atrioventricular valves and surrounding fluid vibrations as
valves close at beginning of ventricular systole

97.  S2- second sound closure of aortic and pulmonary
semilunar valves at beginning of ventricular
diastole
 S3- third sound vibrations of the ventricular walls
when suddenly distended by the rush of blood from
the atria

98. CARDIAC CYCLE
Atrial
Systole
Mitral
Closes
Isovolumic
contract
.
Aortic
opens
S1
Rapid
Ejection
Reduced
Ejection
Isovolumic
Relax.
Aortic
closes
Rapid
Ventricular
Filling
Mitral
opens
S2
Reduced
Ventricular
Filling
Atrial
Systole
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