During which phase does isovolumetric relaxation occur?

Isovolumetric relaxation occurs during early diastole, which is the phase immediately following ventricular systole when the heart muscle relaxes. During this phase, the ventricles are filled with blood from the atria, but all heart valves are closed. This means that the volume of blood in the ventricles remains constant (isovolumetric), while the pressure in the ventricles decreases as the muscle relaxes.

This phase is crucial for allowing the ventricles to prepare for filling without any backflow of blood, ensuring efficient circulation and proper cardiac function. The pressure drop allows the atrioventricular valves to open once the ventricular pressure falls below atrial pressure, facilitating the next phase of filling. Understanding isovolumetric relaxation and its timing within the cardiac cycle is essential for grasping how the heart efficiently manages blood flow and maintains circulation during different phases of contraction and relaxation.