The cardiac cycle 3 basic events are
1.LV contraction
2.LV relaxation
3.LV filling

The function of the heart is to maintain a constant circulation of blood throughout the body. The heart acts as a pump and its action consists of a series of events known as the cardiac cycle. During each heart beat, the heart contracts(SYSTOLE) and relaxes (DIASTOLE). Each cycle lasts about 0.8 second


LV CONTRACTION: LV pressure in the early contraction phase builds up and exceed,that in the left atrium (normally 10-15mmHg), followed about 20sec later by M1, the Mitral component of the first heart sound. Shortly there after pressure changes in the RV, cause the tricuspid valve to close there by creating T1,which is the second component of the first heart sound.
During this phase of contraction, between the MV closure and Aortic valve opening the LV volume is fixed (Isovolumetric contraction) because both the AV and MV are shut. When the pressure in the LV exceeds that in the aorta, the AV opens. Opening of the AV is followed by the phase of ‘Rapid Ejection. The LV Pressure rises to a peak and then starts to fall.

LV RELAXATION: The rate of ejection of blood from the LV into the aorta falls (phase of reduced ejection). The Pressure in the Aorta exceeds the falling pressure in the LV. The AV closes, creating the first component of the second heart sound A2.

LV FILLING: As the LV pressure drops below that in the LA, the MV opens, the phase of rapid filling or early filling occurs to account for most of the ventricular filling. Active diastolic relaxation of the ventricle also contributes to early filling such rapid filling may cause the physiological Third heart sound(S3) particularly when there is hyper kinetic circulation. As pressure in the atria and ventricles equalize,LV filling partially stop (Diastasis).


Atrial systole-0.1s
Atrial diastole
Ventricular systole-0.3s
ICT-0.05s(closure of AV valve to opening of SL valve)
Reduced Ejection-0.14s
Ventricular Diastole-0.5s
Protodiastole-0.04s(combined atrial and ventricular diastole)
IVRT-0.08s(closure of SL valve to opening of AV valve)
First rapid filling-0.113s
Diastasis(slow filling)-0.167s
Last rapid filling-0.1s

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