What is the period during the cardiac cycle when the ventricles are completely closed and blood volume in them remains constant as the ventricles contract?

The period during the cardiac cycle when the ventricles are completely closed, and the blood volume within them remains constant while the ventricles contract, is known as the isovolumetric contraction phase. During this phase, the ventricles contract with their valves closed, leading to an increase in pressure within the ventricles. However, since both the aortic and pulmonary valves are closed, no blood is ejected into the arteries, and the volume of blood in the ventricles does not change. This phase occurs after the atrioventricular valves have closed and before the semilunar valves open, marking a critical moment for creating the necessary pressure to begin ejecting blood into the systemic and pulmonary circulation.

In contrast, the ventricular ejection phase follows this contraction and occurs when the pressure in the ventricles exceeds the pressure in the arteries, allowing the ventricles to eject blood. Atrial systole refers to the contraction of the atria, which occurs before ventricular contraction, and isovolumetric relaxation occurs after ventricular ejection when the ventricles are relaxing and the valves are closed again, leading to a decrease in pressure without a change in volume.