The cardiac cycle describes the regular relaxation and contraction of the heart. It consists of systole, when the ventricles contract to pump blood out of the heart, and diastole, when the ventricles relax and refill. During systole, the atrioventricular valves are closed and semilunar valves are open to allow blood to be ejected from the ventricles. During diastole, the atrioventricular valves open to allow blood to fill the ventricles passively from the atria as well as actively when the atria contract. The cycle repeats approximately 60-80 times per minute.

1. Cardiac Cycle

2. Blood Flow Through Heart

3. Definitions
• Systole = period of ventricular contraction.
• Diastole = period of ventricular relaxation.
• NOTE: Normally diastole is longer than
systole.

4. Cardiac cycle
• General Principles.
• 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.

5. CARDIAC CYCLE
• The normal duration of the cardiac cycle is 0.8
second.
• Each beat of the heart consists of systole and
diastole of atria and ventricles.
• Systole is the contraction of the heart during which
blood is ejected out from the heart
• Diastole is the relaxation of the heart during which
the chambers of the heart are filled with blood

6. • Ventricular Systole:
1. Isovolumetric contraction phase - 0.05 sec
2. Rapid Ejection phase - 0.10 sec
3. Reduced Ejection phase - 0.15 sec

7. Ventricular diastole
1. Proto diastolic phase - 0.04 sec
2. Isovolumetric Relaxation phase - 0.06 sec
3. First Rapid filling phase - 0.10 sec
4. Slow Filling - 0.20 sec
5. Last Rapid Filling Phase - 0.10 sec

8. FACTS TO REMEMBER
• SYSTOLE IS CONTRACTION
-THE RISE IN PRESSURE IN THE CONTRACTING
CHAMBER
-BLOOD BEING EJECTED BY THE CONTRACTING
CHAMBER
• DIASTOLE IS RELAXATION
- A FALL IN PRESSURE OF THE RELAXING
CHAMBER
- FILLING OF THE RELAXING CHAMBER

9. AV valves*
Semilunar
valves†
Status of ventricles and atria
1.Late diastole open closed
• whole heart is relaxed
• ventricles are expanding and filling (passive filling,
~80% of volume)
2. Atrial systole open closed
• atria contract and pump blood
• additional 10–40% filling of ventricles due to active
contraction of atria
3.Isovolumic
ventricular
contraction
closed closed
• ventricular myocytes begin to contract
• ventricle volume unchanged
4.Ventricular
ejection
closed open
• ventricles fully contract
• pump blood to rest of body
5.Isovolumic
ventricular
relaxation
closed closed
• ventricles relax
• ventricle volume unchanged
• atria expand and are filling
* AV (atrioventricular) valves:
1) mitral valve – between the left atrium and the left ventricle
2) tricuspid valve – between the right atrium and the right ventricle
† Semilunar valves:
1) aortic valve – between the left ventricle and the aorta

10. 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.

11. ISOVOLUMETRIC CONTRACTION
Heart
• At the beginning AV valve is open and
semilunar valve is closed. Due to
contraction,IV pressure increases and
blood tries to enter the atrium.
• It is prevented by closure of AV valve
producing 1st heart sound .
• The ventricle becomes a closed cavity with
blood.
• The volume of ventricle does not change
with contraction .
• Hence named ISOVOLUMETRIC
CONTRACTION PHASE.

12. RAPID EJECTION
Heart
• Due to the increased
IV pressure than
aorta and pulmonary
artery semilunar
valves open.
• This forces blood to
eject rapidly.

13. REDUCED EJECTION
Heart
• The continued contraction
of the ventricles pushes
the remaining blood into
the aorta and pulmonary
artery slowly.
• 70-90 ml of blood is
pumped out of ventricle
during ventricular systole.
• It is known as stroke
volume.

14. PROTODIASTOLIC PHASE
• In this, ventricles begin to
relax.The AV valve is closed
and semilunar valve is
open.
• As the IV pressure
decreases below the
pressure in aorta and
pulmonary artery, blood
tries to come back.
• It is prevented by closure
of the semilunar valve
producing 2nd heart sound

15. ISOVOLUMETRIC RELAXATION
Heart
• At the beginning of this phase the
AV valves are closed.
• Now ventricle is a closed cavity.
• IV pressure goes below the atrial
pressure

16. FIRST RAPID FILLING
Heart
• The reduced IV pressure causes
opening of AV valves.
• Once the AV valves open,
blood that has accumulated in
the atria flows rapidly into the
ventricles.
• Turbulence to the flow of blood
produces 3rd heart sound .

17. SLOW – FILLING OR DIASTASIS
Heart
• Rest of blood that has accumulated
in the atria flows slowly into the
ventricles.
• In this phase both atria and ventricle
are relaxing.

18. LAST RAPID- FILLING
HEART
• It coincides with atrial
contraction.
• The atrial systole forces
blood from atria to
ventricle.
• Turbulence due to rapid
rush of blood produces
4th heart sound .
• At the end , ventricle
contain 130 ml of blood.
• It is the end – diastolic
ventricular volume.