Why is a semilunar valve needed when blood flows out of the heart mainly by force of contraction?

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Hello doctor! I would like to ask, why is there a need for a semilunar valve when the blood flowing out of the heart is mainly due to the force of the contraction of the heart? Thank you doctor for helping me!
Le Thuy (Ho Chi Minh)
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Hello! To the question "Why is it necessary to have a semilunar valve when blood flows out of the heart mainly due to the force of contraction of the heart", I would like to answer as follows:
The aortic valve will open when the left ventricle pumps blood to the body, the aortic valve The lungs open when the right ventricle pumps blood to the lungs for oxygen exchange. After pumping is complete, the left and right ventricles have only a small amount of blood left. The left and right ventricles are refilled with blood for the next pump from the left atrium and right atrium, respectively. Without the aortic valve and the pulmonary valve closed, the blood initially pumped from the left and right ventricles will back up into the left and right ventricles, rendering the pump ineffective.
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Answered by Master, Doctor Danh Man - Cardiologist - Department of Medical Examination & Internal Medicine - Vinmec Phu Quoc International General Hospital