Which statement is true regarding blood volume in the ventricles during IVRT?

During isovolumetric relaxation time (IVRT), the ventricles are in a state where both the aortic and pulmonary valves are closed, leading to a period of ventricular relaxation without any change in volume. This phase occurs after the ventricles have ejected blood into the aorta and pulmonary artery and before the mitral and tricuspid valves open to allow for filling from the atria.

During this time, the ventricular pressures drop but there is no blood flow in or out of the ventricles, resulting in a stable volume within the ventricles. Thus, the correct statement highlights that the volumes do not change during IVRT because both the contraction of the myocardium and the valves' closure prevent any volume fluctuation. This understanding of IVRT is critical for interpreting echocardiography findings and the hemodynamics of the heart, especially in relation to diastolic function.