Final answer:
Isovolumetric contraction is the phase of systole where the ventricular pressure rises but is not yet high enough to open the aortic valve, thus keeping it closed.
Step-by-step explanation:
During the phase of ventricular systole where the aortic valve remains closed is known as the isovolumetric contraction. This occurs initially as the ventricles contract and the pressure within them rises. However, this pressure is not high enough to open the aortic valve that leads to the aorta. The valve stays shut until the pressure in the ventricles exceeds the pressure in the aorta, at which point the aortic valve opens, and blood is ejected from the heart. The closing of the tricuspid and mitral valves due to increased pressure, along with the aortic valve being closed, indicates that the volume within the ventricles remains constant. Therefore, the isovolumetric contraction phase precedes ventricular blood ejection and is different from the ventricular ejection phase, which occurs once the ventricular pressure exceeds aortic pressure and the aortic valve opens allowing for the ejection of blood.