This document summarizes the cardiac cycle, which consists of one systole and one diastole phase. It describes the durations of atrial systole, atrial diastole, ventricular systole, and ventricular diastole. It then provides details on the pressure and volume changes that occur in the left atrium, left ventricle, and aorta during each phase of the cardiac cycle, including atrial systole, isovolumetric contraction, rapid ventricular ejection, slow ventricular ejection, isovolumetric relaxation, rapid passive ventricular filling, and slow passive ventricular filling. Pressure changes throughout the cardiac cycle are also discussed.

1. CARDIAC CYCLE
P.BALA NANDA
Assistant Professor
Department of Physiology
GIMSR, GITAM University

2. CARDIAC CYCLE = 1 SYSTOLE + 1 DIASTOLE
CARDIAC CYCLE =
60 sec 60
-------------- = ------------ = 0.833 sec
HR 72
STUDY IN THE LEFT HEART CHAMBERS with DURATIONS
ATRIAL SYSTOLE : 0.1 sec
ATRIAL DIASTOLE : 0.7 sec
VENTRICULAR SYSTOLE : 0.3 sec
VENTRICULAR DIASTOLE : 0.5 sec
CARDIAC CYCLE

3. CARDIAC CYCLE – ATRIAL SYSTOLE
1
2
3
1. Changes that occur during this phase in Left
atrium, Ventricle and Aorta (1,2,3)
2. 80% of the ventricle is already filled with blood
(Passive filling)
3. 20% of the blood is contributed by Atrium when
contracted
4. During contraction of Atrium the pressures in the
atrium is high when compared with Ventricle.
5. Due to increased pressure in atrium the mitral
valve (AV valves ) opens and blood flows to the
ventricle.
6. Due to this the Pressure in the ventricle increases
to 5- 8 mmofHg.
7. During the contraction of atrium and the
pressures in atrium forms a pressure wave called
“a”.

4. CARDIAC CYCLE- ISOVOLUMETRIC CONTRACTION
1. Due to ventricle contraction increase in pressure from 0 mm of Hg to 5 mm of Hg in the
ventricle forces the blood back to atria (due to decrease in pressure) this closes the Mitral
Valve/ AV Valves causing 1st Heart sound (S1).
2. Ventricle starts to contract in closed chamber because of closed AV and Aortic Valves (due
to less pressure in Ventricle) hence called “ISOVOLUMETRIC CONTRACTION”
3. Due to continous contraction of ventricle pressure in the ventricles increases to 80 mm of
Hg.
4. Due to closure of Mitral valve a little jerk/ pressure is Produced forms a pressure wave “
c”.
5. During this phase The atrium is filling with the blood from the lungs & aotra is pushing the
blood due to its elasticity
DUE TO CLOSURE OF
AORTIC AND AV VALVES
THE VENTRICLE IS A
CLOSED STRUCTURE

5. CARDIAC CYCLE- RAPID VENTRICULAR EJECTION PHASE
1. On attaining the maximum pressure in the ventricle (81 mm of Hg) the Valves in
the aorta (80 mm of Hg) opens and the blood oozes rushes into great vessel
forming the aorta to stretch. The stretching of aorta and ventricle appears as same
chamber.
2. At this Phase the pressure in the Ventricle reaches to 120 mm of Hg along with the
Aorta.
3. The atrium acts like a reservoir and receives the blood from Lungs causing
increase in pressure forming “ C “ wave.
CONSIDER ONLY LEFT SIDE OF THE
HEART (LEFT ATRIUM,LEFT VENTRICLE
AND AORTA)

6. CARDIAC CYCLE- SLOW VENTRICULAR EJECTION PHASE
1. In this phase the Atrium is receiving the blood.
1. The pressure wave “ C” continue to record at this phase.
1. The Ventricle is pumping blood into the aorta with a reduced speed.
1. The Ventricle remains in a contracted state, but the pressures in the ventricle
gradually falls below 120 mm of Hg
CONSIDER ONLY LEFT SIDE OF THE HEART (LEFT
ATRIUM,LEFT VENTRICLE AND AORTA)

7. CARDIAC CYCLE- ISOVOLUMETRIC RELAXATION PHASE
1. When the ventricle is relaxing intra ventricular pressure falls. This causes the
pressure in the aorta is decreased causing the blood to fall back into ventricle.
This causes the closure of Aortic valves forms second heart sound “S2”
2. The pressure in the ventricle tends to fall while relaxing , but even though the
pressures in the ventricle is more than Atrium.
3. The Ventricle in this phase relaxes as a closed chamber.
4. The atrium still continue to receive the blood from the Lungs increases the
pressure in the atrium
Note : The AV Valves and
Aortic valves are closed.
There will be decreasing in
the ventricular pressureCONSIDER ONLY LEFT SIDE OF THE
HEART (LEFT ATRIUM,LEFT
VENTRICLE AND AORTA)

8. CARDIAC CYCLE- RAPID PASSIVE VENTRICULLAR FILLING PHASE
1. After the previous Ventricular Systole/ Ejection some of the blood remains in the Ventricle
called “ END SYSTOLIC VOLUME (ESV)”.
2. The pressures in the ventricle is much more decreases and the atrial pressure is increased
due to filling of blood from the Lungs.
3. This causes the mitral valve to open. Due to high pressure in the atrium the blood from the
atrium rapidly falls in to Ventricle even it is not contracting. This is called Passive filling.
4. Hence this phase is called RAPID PASSIV VENTRICULAR FILLING PHASE (RPVF)
CONSIDER ONLY LEFT SIDE OF THE
HEART (LEFT ATRIUM,LEFT VENTRICLE
AND AORTA)

9. CARDIAC CYCLE- SLOW PASSIVE VENTRICULAR FILLING PHASE
1. After Cumulative blood (ESV & RPVF) falls, The venous blood from the lungs Directly
fall into the Ventricle because the Mitral valve is already open. Hence, the Atrium is no
longer acting as a reservoir.
2. Hence this phase is called SLOW PASSIVE VENTRICULAR FILLING PHASE
(SPVF) or DIASTASIS
3. The SA node starts to fire after this phase and the cycle continues with starting
“ATRIAL SYSTOLE”
CONSIDER ONLY LEFT SIDE OF THE HEART (LEFT
ATRIUM,LEFT VENTRICLE AND AORTA)

10. PRESSURE CHANGES DURING CARDIAC CYCLE
VERY IMPORTANT READ FROM BOOK IN EASY METHOD

11. THANK YOU