THORAX ABDOMEN AND PELVIS

Detailed explanation-1: -Diastole is the relaxation phase of the heartbeat. During this phase, the ventricles relax and blood flows through the left and right atria from the vena cava and pulmonary veins. Systole is the contraction phase of the heartbeat.

Detailed explanation-2: -The cardiac cycle involves four major stages of activity: 1) “Isovolumic relaxation", 2) Inflow, 3) “Isovolumic contraction", 4) “Ejection".

Detailed explanation-3: -Since the atrioventricular valves remain closed at this point, there is no change in the volume of blood in the ventricle, so the early phase of ventricular diastole is called the isovolumic ventricular relaxation phase, also called isovolumetric ventricular relaxation phase (see image below).