During the isovolumetric relaxation time (IVRT), what happens to the ventricular pressures?

During the isovolumetric relaxation time (IVRT), which occurs after the closure of the aortic and pulmonary valves, the ventricles are not actively filling with blood. Instead, the ventricular muscle is relaxing, and the pressures within the ventricles are decreasing as the heart transitions from systole to diastole.

As the ventricles relax, the pressure inside them drops significantly because the ventricular muscle fibers are elongating and there is no volume change since all valves are closed; hence, no blood can enter or leave the ventricles. This marked reduction in pressure prepares the ventricles for the subsequent phase of diastole when the mitral and tricuspid valves open, allowing passive filling from the atria.

Therefore, during IVRT, the expected behavior is a continuous decrease in ventricular pressures, which helps facilitate the transition to filling. Understanding this phase is vital as it reflects the ventricular compliance and influences overall diastolic function.