CardiacCycle
Dr. Muhammad Usman Hashmi

CARDIACCYCLE
A single cycle of cardiac activity can be divided into two basic phases:
Diastole (Represents the period of time when the ventricles are relaxed).
Systole (Represents the time during which the left and right ventricles contract
and eject blood into the aorta and pulmonary artery).
The cardiac cycle is usually divided into seven phases:
Phase 1 - Atrial Contraction
Phase 2 - Isovolumetric Contraction
Phase 3 - Rapid Ejection
Phase 4 - Reduced Ejection
Phase 5 - Isovolumetric Relaxation
Phase 6 - Rapid Filling
Phase 7 - Reduced Filling

CARDIACCYCLE

1- ATRIALCONTRACTION
 It is initiated by the P wave (Depolarization of the atria).
 As the atria contract  the pressure in atria increases  which forces more
blood flow across the open atrioventricular (AV) valves  leading to a rapid
flow of blood into the ventricles.
 Atrial contraction produce a small increase in AP which represent as "a-
wave"
 Atrial contraction (fourth heart sound, S4).

2- ISOVOLUMETRICCONTRACTION
 All valves are closed (Allow ventricle build pressure)  Mitral valve will bulge back
(C wave)  build pressure in the ventricles (should exceed 80 mmhg).
This phase represented in ECG as QRS wave (Ventricular depolarization).
 Closure of the AV valves results in the first heart sound (S1).

3- RAPIDANDSLOWEJECTION
PHASES.
 Ventricular pressure exceed (80 mmhg)  Aortic and Pulmonic Valves Open  rapid
ejection.
 A and P Valves Open; AV Valves Remain Closed (blood filling in the atrium  but
still closed).
 After200 msec ventricular pressure start falling down + aortic pressure falling down
 slow ejection.
 No heart sounds are ordinarily noted during ejection.

4- ISOVOLUMICRELAXATION
 T wave represent the repolarization of ventricles  there will be falling of
ventricular pressure  A and P valves closed (make S2).
Left atrial pressure (LAP) continues to rise because of venous return from the
lungs. The peak LAP at the end of this phase is termed the v-wave.

5- RAPIDANDSLOWPASSIVE
VENTRICULARFILLING
 The mitral valve is open  the blood fill the ventricle without atrial contraction we
get ventricular filling the blood come back from the body and lungs cause
ventricular filling.
 The volume increases until the p wave occur and the next cycle start
 Ventricular filling is normally silent. When a third heart sound (S3)??

SUMMARY
Cardiac cycle is single cycle that represent systole and
diastole.
The cardiac cycle is usually divided into seven
phases:
Phase 1 - Atrial Contraction
Phase 2 - Isovolumetric Contraction
Phase 3 - Rapid Ejection
Phase 4 - Reduced Ejection
Phase 5 - Isovolumetric Relaxation
Phase 6 - Rapid Filling
Phase 7 - Reduced Filling