Cardiac cycle is defined as the succession of coordinated events taking place in the heart during each beat. Each heart beat consists of two major periods called systole and diastole.

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3. o Cardiac cycle is defined as the succession of coordinated events taking
place in the heart during each beat.
o Each heart beat consists of two major periods called systole and diastole.
o During systole heart contracts and pumps the blood through arteries.
o During diastole heart relaxes and blood is filled in the heart.
o All these events are repeated in a cyclic manner.
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4. i. Atrial Events
ii. Ventricular Events
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5. When the heart beats at a normal rate of 72/minute duration of each cardiac
cycle is about 0.8 seconds.
o Atrial Events
Atrial Systole= 0.1 sec
Atrial Diastole= 0.7 sec
o Ventricular Events
Ventricular Systole= 0.3 sec
Ventricular Diastole= 0.5 sec
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6. o Atrial Systole is also known as last rapid filling phase or presystole.
o It is usually considered as the last phase of ventricular diastole.
o The duration is 0.11 sec.
o During this period, only a small amount, i.e. 10% of blood is forced from
atria into ventricles.
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7. o Atrial diastole starts after atrial systole.
o Simultaneously ventricular systole also starts.
o Atrial diastole last for about 0.7 sec.
o The long atrial diastole is necessary because this is the period during which
atrial filling takes place.
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8. o Isometric Contraction Period
o Ejection Period
o Proto Diastole
o Isometric Relaxation Period
o Rapid Filling Phase
o Slow Filling Phase
o Last Rapid Filling Phase
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9. o It is the phase of ventricular systole.
o It lasts for 0.05 sec.
o This is a type of muscular contraction characterized by increase in tension,
without any change in the length of muscle fibres.
o Immediately after atrial systole, the antrioventricular pressure valves are
closed due to increase in ventricular pressure.
o Semilunar valves are already closed.
o Now ventricles contract as closed cavities.
o In such a way there is no change in the volume of ventricular chambers or in
the length of muscle fibres.
o Only the tension increases in ventricular musculature.
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10. o Due to the opening of semilunar valves and isotonic contraction of
ventricles, blood is ejected out of both the ventricles.
o Hence this period is called as ejection period.
o Duration= 0.22 sec
o Ejection period is of two stages:
 1st Stage: Rapid Ejection Period
o 1st stage starts immediately after the opening of semilunar valves.
o During this stage, a large amount of blood is rapidly ejected from both the
ventricles. It lasts for 0.13 sec
 2nd Stage: Slow Ejection Period
o During this stage, the blood is ejected slowly with much less force.
o Duration of this period is 0.09 sec.
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11. o It is the first stage of ventricular diastole, hence the name protodiastole.
o Duration= 0.04 sec.
o Due to the ejection of blood, the pressure in aorta and pulmonary artery
increases and pressure in ventricle drops.
o When intraventricular pressure becomes less than the pressure in aorta and
pulmonary artery, the semilunar valves close.
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12. o It is a type of muscular relaxation characterized by decrease in tension
without any change in the length of the muscle fibres.
o During this period, once again all the valves of the heart closed once again.
o Intraventricular pressure decrease.
o Duration= 0.08 sec.
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13. o When AV- Valves are opened, there is sudden rush of blood from atria into
ventricles.
o So, this period is called the first rapid filling period.
o Ventricles also relax isotonic alloy about 70% of filling takes place during
this phase, which last for 0.11 sec.
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14. o After the sudden rush of blood, the ventricular filling becomes slow. Now it is
called slow filling.
o It is also called as diastatis.
o About 20% of filling occurs in this phase.
o Duration= 0.19 sec.
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15. o Last rapid filling phase occurs because of atrial systole.
o After slow filling period, the atria contract and push a small amount of blood
into ventricles.
o About 10% of ventricular filling takes place during this period.
o Flow of additional amount of blood into ventricles due to the atrial systole is
atrial kick.
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17. “Heart sounds are produced by the heart during a cardiac cycle, specifically
when heart valves snap shut”
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18. 1. First heart sound (S1)
2. Second heart sound (S2)
3. Third heart sound (S3)
4. Fourth heart sound (S4)
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19. o It is heard dull and prolonged often described ad “LUB”.
o It occurs at the beginning of ventricular systole.
o It is generated due to closure of Atrio Ventricular valves.
o Its frequency is 30-80 cps.
o It varies from 0.09s to 0.16s and average 0.14s.
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20. o It is sharp and short usually described ad “DUB”.
o It occurs at the end of ventricular systole.
o Its frequency is 150-200 cps.
o Its duration is 0.11s.
o It is generated due to closure of semilunar valves.
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21. o It is heard occasionally and weak and rumbling in nature.
o It occurs at the beginning of middle third of the diastole.
o Its frequency is below 40 cps.
o It is generated due to the oscillation of blood back and forth between the
walls of the ventricles and is initiated by inrushing blood from atria.
o It is in youth, athletes and in pregnancy.
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22. o It is weak and rumbling.
o It can’t be observed with stethoscope but can be recorded on
phonocardiogram.
o It occurs when atria contracts.
o Its frequency is 20 cps.
o Its sound is similar to those of third heart sound.
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