Final answer:
The ventricular systole phase of the cardiac cycle is when the semilunar valves are open, allowing blood to be ejected from the ventricles into the pulmonary trunk and aorta.
Step-by-step explanation:
The period of time when the semilunar valves are open and blood flows out of the ventricles is known as the ventricular systole phase of the cardiac cycle. This phase occurs when the ventricles contract and eject blood into the pulmonary trunk and aorta. During this phase, the atrioventricular valves are closed to prevent backflow of blood into the atria.
The open semilunar valves, comprising the pulmonary and aortic valves, allow blood to flow out of the heart and into the circulation. As the ventricles contract, the pressure within them rises above the pressure in the pulmonary trunk and aorta, which forces the semilunar valves to open and blood to be ejected. This vital phase is crucial for maintaining effective circulation and ensures that oxygenated blood is delivered to the body and deoxygenated blood is sent to the lungs for oxygenation.