The document defines the cardiac cycle and describes the stages and events that occur during one full heartbeat. It discusses the pressure and volume changes that take place in the heart's chambers and valves over the course of the cardiac cycle. The cycle includes atrial systole, ventricular systole, and relaxation. During atrial systole the atria contract, pushing blood into the ventricles. In ventricular systole the ventricles contract, pumping blood out of the heart. Relaxation allows the chambers to refill before the next cycle begins. Each ventricle expels around 70mL of blood per beat, with the left ventricle pumping blood to the aorta and the right ventricle to the pulmonary trunk.

2. GUESS
MY
TOPIC…?
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3. 3

4. CARDIAC
CYCLE
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5. LEARNING OBJECTIVE
• Define cardiac cycle
• Describe the pressure and volume
changes during cardiac cycle
• Explain the stages of cardiac cycle
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6. INTRODUCTION
• At rest, the healthy adult heart is likely to
beat at a rate of 60-90 beats per minute.
• A single cardiac cycle includes all the
events associated with one heart beat.
• Thus, a cardiac cycle consist of systole
and diastole of ventricles.
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7. DEFINITION
“The complete sequence of events in the
heart from the beginning of one heart
beat to the beginning of following beat:
a complete heartbeat including systole
and diastole”.
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8. PRESSURE AND VOLUME
CHANGES DURING
CARDIAC CYCLE
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9. • In each cardiac cycle, the atria and ventricles
are directly contract and relax forcing blood
from areas of higher pressure to areas of
lower pressure.
• As a chamber of heart contracts blood
pressure within it increases.
• So it shows relation between heart’s electrical
signals (ECG) and changes in atrial pressure,
ventricular pressure, aortic and ventricular
volume during cardiac cycle.
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10. Conti…
• So the pressure apply to left side of heart ;
pressure on right side are considerably lower.
• Each ventricles expels same volume of blood
per beat and same pattern exists for both
pumping chambers.
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11. STAGES
OF
CARDIAC CYCLE
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12. • To take 74 beats per minute, as an example
each cycle last about 0.8 second and consist
of :
• Atrial Systole – contraction of atria
• Ventricular systole – contraction of
ventricles
• Complete cardiac diastole – relaxation of
atria and ventricles
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13. ATRIAL SYSTOLE
• During atrial systole, which lasts about
0.1 second, the atria are contracting. At
the same time, the ventricles are relaxed.
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14. Conti…
1. Depolarization of SA node causes atrial
depolarisation, marked by P wave in ECG.
2. Atrial depolarization causes atrial systole.
As the atria contract, they exert pressure on
blood within, which forces blood through
the open AV valves into ventricles.
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15. Conti…
3. Atrial systole contributes a final 25ml of
blood to the volume already in each
ventricles about (105 ml). The end of atrial
systole is also end of ventricular diastole
(relaxation). Thus, each ventricle contains
about 130ml at end of its relaxation period
(diastole). This blood volume is called end
diastolic volume (EDV).
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16. Conti…
4. The QRS complex in ECG marks the
onset of ventricular depolarisation.
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17. VENTRICULAR SYSTOLE
• During ventricular systole, which lasts
about 0.3 second, the ventricles are
contracting. At the same time, the atria
are relaxed in atrial diastole.
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18. 5. Ventricular depolarization causes ventricular
systole. As ventricular systole begins,
pressure rises inside the ventricles and
pushes blood up against atrioventricular
(AV) valves, forcing them shut. For about
0.05 seconds, both the SL (semilunar) and
AV valves are closed. This is the period of
isovolumetric contraction. During this
interval, cardiac muscle fibers are
contracting and exerting force but are not yet
shortening.
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19. Conti…
• Thus, the muscle contraction is isometric
(same length). Moreover because all four
valves are closed, ventricular volume
remains the same (isovolumic).
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20. Conti…
6. Continued contraction of ventricles causes
pressure inside the chambers to rise sharply.
When left ventricular pressure surpasses
aortic pressure at about 80 mmHg and right
ventricular pressure rises above the pressure
in the pulmonary trunk (about 20 mmHg),
both SL valves open. At this point, ejection
of blood from the heart begins. The period
when SL valves are open is ventricular
ejection and lasts for about 0.25 sec.
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21. Conti…
• The pressure in the left ventricle
continues to rise to about 120 mmHg,
whereas the pressure in the right
ventricle climbs to about 25-30 mmHg.
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22. Conti…
7. The left ventricle ejects about 70 ml of
blood into the aorta and the right ventricle
ejects the same volume of blood into the
pulmonary trunk. The volume remaining in
each ventricle at the end of systole, about 60
ml, is the end- systolic volume (ESV).
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23. Conti…
• Stroke volume, the volume ejected per
beat from each ventricle, equals end
diastolic volume minus end systolic
volume.
SV = EDV-ESV
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24. Conti…
• At rest, the stroke volume is about
SV = 130ml - 60ml = 70ml
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25. Conti…
8. The T wave in the ECG marks the onset of
ventricular repolarisation.
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26. RELAXATION PERIOD
• During relaxation period, which lasts
about 0.4 second, the atria and ventricles
are both relaxed. As the heart beats faster
and faster, the relaxation period becomes
shorter and shorter, whereas the
durations of atrial systole and ventricular
systole shorten only slightly.
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27. Conti…
9. Ventricular repolarisation causes ventricular
diastole. As the ventricles relax, pressure
within the chambers falls and blood in the
aorta and pulmonary trunk begins to flow
backward toward the regions of lower
pressure in the ventricles. Backflowing of
blood catches in the valve cusps and closed
the SL valves.
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28. Conti…
• The aortic valve closes at a pressure of about
100mmHg. Rebound of blood off the closed
cusps of the aortic valve produces the
dicortic wave on the aortic pressure curve.
After the SL valves close, there is a brief
interval when ventricular blood volume
doesnot change because all four valves are
closed. This is the period of isovolumetric
relaxation.
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29. Conti…
10. As the ventricles continue to relax, the
pressure falls quickly. When ventricular
pressure drops below atrial pressure, the AV
valve open, and ventricular filling begins.
The major part of ventricular filling occur
just after AV valves open.
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30. Conti…
• Blood that has been flowing into and
building up in the atria during ventricular
systole then rushes rapidly into ventricles. At
the end of relaxation period, the ventricles
are about three quarters full.
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31. • The P wave appears in ECG, signalling
the start of another cardiac cycle.
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32. ANY QUERIES?
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37. • How Much Amount Of Blood Ventricles
Expels Per Beat?
• Do The Right And Left Ventricles
Pump The Same Amount Of Blood?
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