Cardiovascular System - Cardiac Cycle

Handout of Cardiac Cycle

• Prepared by Dr. Magdi El Sersi

Atrial Systole



Both atria contract

1)

2)

3)

4)

5)

6)

7)

Atrial pressure: initially increases then it decreases again.

Ventricular pressure: initially increases slightly then it decreases

again (due to dilatation of the ventricle).

Ventricular volume: this increases slightly due to ventricular dilatation.

Valves: the A-V valves are open while the semilunar valves are

closed.

Aortic pressure: this decreases gradually due to continuous blood

flow from the aorta to the peripheral vessels.

Sounds: the 4th heart sound is recorded in this phase.

ECG: the P wave starts about 0.02 sec before this phase, while the

main part of the P wave, the P-R segment and the Q wave occur

during it.

Isovolumetric contraction phase



Early phase of ventricular systole in which the ventricles

contract but no ejection occurs.

1)

2)

3)

4)

5)

6)

Ventricular pressure & volume: the ventricles contract isometrically,

the left ventricular pressure rises sharply to 80 mmHg and the

ventricular volume remains unchanged .

valves: the A-V valves are closed because the ventricular pressure

exceeds the atrial pressure and the semilunar valves also remains

closed thus all valves are closed in this phase and the ventricles

become closed chamber .

sounds: the early component of the first heart sound is heard in this

phase due to the closure of the A-V valves.

Atrial pressure: on closure of the A-V valves, their cusps bulge into

the atria leading to a slight increase in the atrial pressure .

Aortic pressure: this decreases to a minimum of about 80 mmHg at

the end of this phase, which is called the diastolic blood pressure.

ECG: the Q wave starts about 0.02 sec before this phase, while the R

and S waves occurs during it.

Maximum ( Rapid) ejection phase



The semilunar valves open and blood is ejected into the great

arteries.

1)

2)

3)

4)

5)

6)

Ventricular...