The cardiac cycle describes the sequence of events in the heart from one heartbeat to the next. It involves the coordinated contractions and relaxations of the atria and ventricles. There are seven phases in the cardiac cycle: 1) atrial systole, 2) isovolumetric ventricular contraction, 3) rapid ventricular ejection, 4) slow ventricular ejection, 5) isovolumetric ventricular relaxation, 6) rapid ventricular filling, and 7) slow ventricular filling. The cycle ensures blood is pumped efficiently from the heart to the lungs and body.

1. CARDIAC CYCLE
Dr Sutapa Datta
Assistant Professor of Zoology
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2. CARDIAC CYCLE
Definition:
The cardiac events that occur from the beginning of
one heartbeat to the beginning of the next are called
the cardiac cycle.
oSystole and diastole of atria and ventricles alternately
contract and relax
 During atrial systole, ventricles are relaxed
 During ventricle systole, atria are relaxed
oForces blood from higher Pressure to lower Pressure
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3. 1.Atrial systole(0.11s-0.53s)
2. Isovolumetric ventricular contraction (0.05s)
3. Rapid ventricular Ejection Phase (0.22-0.27s)
4. Slow ventricular Ejection Phase (0.22-0.27s)
5.Isovolumetric ventricular relaxation(0.08s)
6. Rapid Passive Ventricular filling Phase (0.11s)
7. Slow Passive Ventricular filling Phase (0.19s)
There are seven phases of the cardiac cycle (and duration of
phases):
(Systole-
when the
ventricles
are
contracting)
(Diastole-
when the
ventricles
are
relaxing)
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4. 1.Atrial systole(0.11s-0.53s)
2. Isovolumetric ventricular contraction (0.05s)
3. Rapid ventricular Ejection Phase (0.22-0.27s)
4. Slow ventricular Ejection Phase (0.22-0.27s)
5.Isovolumetric ventricular relaxation(0.08s)
6. Rapid Passive Ventricular filling Phase (0.11s)
7. Slow Passive Ventricular filling Phase (0.19s)
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Phases of the cardiac cycle

5. 1. Atrial Contraction
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LEFT ATRIUM
Before atrial contraction 80% of Ventral
filling done
20% by atrial contraction (required during
exercise)
Atria contract- intraatrial Pressure
increases
(a wave)- blood moves to LV - Pressure
transferred to LV
LV
Before atria contracts- Pressure in LV is 0 –
LV in relaxed cond- start of atria contraction
slight increase in Pressure LV
AORTA
Aortic valves remain closed
Pressure in aorta is more than LV

6. 2. Isovolumetric contraction
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LEFT ATRIUM
•As Pressure in LV increases more than LA
•Mitral valve closes- a slight increase (jerk) in
Pressure in LA
(c wave)
Blood from lungs still coming- Pressure started to
build up slightly- start of v wave
LV
•LV starts contraction- intraventricular Pressure
build up- more than LA
•Mitral valve closed- S1 (tricuspid in RA also
closed, both closure at the same time)
•Pressure not that enough to open aortic valve
•Contracts as closed chamber- blood vol and
Pressure remain same- isovolumic, isometric;
isovolumetric contraction (no blood leaving, no
blood coming)
• Pressure same as aorta
AORTA
Pressure still more than LV
Aortic valve closed

7. 3. Rapid Ventricular Ejection Phase
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•LV
•Pressure reaches to 81 mm of Hg more than
aorta – aortic valves open- termination of IVC
•Next phase RVEP
•Still contraction
•Pressure reaches to 120 mm of Hg
•Blood rushes to aorta
•AORTA
•Aorta elastic, dilates- huge ventricular inflow
•Aorta and LV having same Pressure
•Act as a same chamber
RVEP cannot last long
•LA
•Receiving blood from lungs
•reservoir

8. 4. Slow Ventricular Ejection Phase
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•LV
•Pressure more than LA- mitral valve still
closed
•Still contracting
•Aortic valve still opened
•Pressure starts falling- bcoz blood flow to
aorta
•Ejection rate slow- SEP / SVEP
•Still Pressure more than aorta- blood flow,
but slow
•AORTA
• Pressure decreases as that of LV
•LA
•Still getting blood from lungs

9. 5. Isovolumetric relaxation
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LV
1. Pressure falls
2. Aortic blood tries to backflow- closure of
aortic valve- S2 (both aortic and pulmonary valves,in RV,
closed with sound, but aortic closure is slightly earlier)
3. Pressure less than aorta but still more than
LA
4. Relaxes as closed chamber – start of IVR
•AORTA
•Pressure more- valves closed
•LA
•Accumulates blood from lungs
•Pressure Less than LV
•Mitral valve closed
•Due course Pressure LA more than LV

10. 6. Rapid Passive Ventricular Filling
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•LV
•After slow ejection, left over blood- ESV
•Pressure less than LA
•LA
•Accumulated blood from LA moves rapidly to
LV- mitral valve opens
•Without atrial contraction
•This is RPVF
•AORTA
•Pressure more than LV

11. 7. Slow Passive Ventricular Filling (Diastasis)
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•LA
•Mitral valve opened-
•atrium not a reservoir- a passage
•directly carry blood passively to LV ,slowly
• Pressure difference less
•This is SPVF
•LV
•Receives blood from LA
•Pressure less than LA
•AORTA
•Pressure still more than LV
•Aortic valves closed

12. Atrial
depolarization
Ventricular
depolarization
Ventricular
repolarization
Atrial systole
begins and
forces blood to
into ventricles
Ventricular
contraction
pushes AV
valves closed
Semilunar
valves open
and blood is
ejected
Semilunar
valves close
and blood
flows into aorta
Chambers
relax and
blood fills
ventricles
passively
Atrial systole
Ventricular systole Ventricular diasystole
1st phase 2nd phase Early Late
PHASES OF CARDIAC CYCLE
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13. THANK YOU
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Reference reading:
1. https://www.cvphysiology.com/Cardiac%20Function/CF024
2. https://www.researchgate.net/figure/Cardiac-cycle-top-diagram-depicting-
cardiac-signals-ECG-Pressureessures-volumes-and_fig6_281383702
3. https://sites.google.com/site/stethoscope2011/physiology
4. https://www.wikiwand.com/en/Wiggers_diagram
5. https://www.wikiwand.com/en/Wiggers_diagram
6. Review of Medical Physiology: Ganong
7. https://www.youtube.com/watch?v=jVvQaqFOJpY&t=2823s