Isovolumetric relaxation and ventricular filling (two phases of the cardiac cycle) take place during . Isovolumetric relaxation and ventricular filling (two phases of the cardiac cycle) take place during . ventricular systole ventricular diastole

Option B, ventricular diastole

Explanation:

Ventricular diastole also termed as ventricular relaxation consists of two phases. In the first phase, the following set of events takes place –  

a)Relaxation of ventricle muscles

b)Reduction in pressure  of blood within the ventricles

c)As this reduced blood pressure gets lower than that of pressure with in the pulmonary trunk and aorta, blood starts flowing back towards the heart.

d)A small dip in the blood pressure is observed at this stage

e)Volume at this stage remains constant as the atrioventricular valves remain closed

f)This phase is known as isovolumic ventricular relaxation phase

In the second phase, the following set of events takes place –

a)Relaxation of ventricular muscle  

b)Dropping of pressure of the  blood within the ventricles lower than that of pressure of blood in the atria

c)Blood starts flowing from atria into the ventricles thereby opening the tricuspid and mitral valves

d)Both the heart chambers chambers are in diastole,  

e)Atrioventricular valves are open

f)Semilunar valves remain closed  

Hence, option B is correct