28. During which phase of cardiac cycle is ventricular volumelowest?A. Isovolumetric ventricular contractionB. Isovolumetric ventricular relaxationC. Atrial systoleD. Rapid ventricular ejection

The ventricular volume is lowest during the phase of Isovolumetric ventricular relaxation (option B).

Here's the step by step explanation:

1. Isovolumetric ventricular contraction: This is the first phase of the cardiac cycle where the ventricles start to contract with the closure of the atrioventricular valves (mitral and tricuspid), but the volume remains constant as the semilunar valves (aortic and pulmonary) are still closed.

2. Rapid ventricular ejection: In this phase, the semilunar valves open due to increased pressure in the ventricles, and blood is ejected out of the ventricles, decreasing the volume.

3. Isovolumetric ventricular relaxation: This is the phase after the ventricles have ejected most of the blood and they start to relax. The semilunar valves close to prevent the backflow of blood, and the volume of the ventricles is at its lowest because most of the blood has been ejected out.

4. Atrial systole: This is the phase where the atria contract to push the remaining blood into the ventricles, increasing the ventricular volume again.

So, the ventricular volume is lowest during the Isovolumetric ventricular relaxation phase.