Final answer:
During the early phase of ventricular diastole, the ventricular muscle relaxes and the pressure on the blood within the ventricle decreases. This is called the isovolumic ventricular relaxation phase.
Step-by-step explanation:
During the early phase of ventricular diastole, the ventricular muscle relaxes and the pressure on the blood within the ventricle decreases. When the pressure within the ventricles drops below the pressure in the pulmonary trunk and aorta, blood flows back toward the heart, resulting in a small dip known as the dicrotic notch in blood pressure tracings. The semilunar valves close to prevent backflow into the heart. Since the atrioventricular valves remain closed at this point, there is no change in the volume of blood in the ventricle. This early phase of ventricular diastole is called the isovolumic ventricular relaxation phase or isovolumetric ventricular relaxation phase.