THORAX ABDOMEN AND PELVIS

Detailed explanation-1: -During the early stages of ventricular diastole, both the atrioventricular and semilunar valves are closed. During this phase, there is no change in the amount of blood in the ventricle, but there is a precipitous fall in the intraventricular pressure. This is known as isovolumetric relaxation.

Detailed explanation-2: -Isovolumetric ventricular contraction (a-b): This phase marks the beginning of systole and starts with the appearance of the QRS complex on the EKG and the closure of the AV valves at point (a).

Detailed explanation-3: -Phase IV: Period of isovolumetric relaxation-both valves are closed and intraventricular pressure decreases without any blood volume changes. The period of relaxation is called diastole in which the ventricle fills with blood and the period of ventricle contraction is called systole.