What phase of the cardiac cycle occurs when the valves are closed and contraction happens without a change in volume?

The phase of the cardiac cycle characterized by closed valves and contraction without a change in volume is known as isovolumetric contraction. During this phase, the ventricles are fully filled with blood, and when they contract, the pressure rises but the volume remains constant because both the atrioventricular (AV) and semilunar valves are closed. This contraction occurs just before the blood is ejected into the aorta and pulmonary artery, resulting in a rapid increase in ventricular pressure as the cardiac muscle fibers contract. Understanding this phase is essential, as it plays a crucial role in the overall efficiency of the heart's pumping mechanism, setting the stage for the subsequent ejection of blood during the ejection phase when the semilunar valves open. Knowing the dynamics of this phase helps in appreciating the mechanics of cardiac function and the importance of pressure changes in the heart’s pumping activity.