![]() ![]() To prevent back flow of blood into the ventricles, the semilunar valves close during ventricular diastole. Contraction of the right ventricle leads to the opening of pulmonary semilunar valve in order to eject blood into the pulmonary trunk (which branches out into the right pulmonary artery and left pulmonary artery) and, hence, the pulmonary circulation. Contraction of the left ventricle leads to the opening of aortic semilunar valve in order to eject blood into the aorta and, hence, the systemic circulation. While the left and right ventricles contract nearly simultaneously, each pumps blood into a different artery. During the relaxation phase of the heart ( diastole), the ventricles are filled with blood in preparation for the next contraction phase. During the contraction phase ( systole), blood is ejected from both the left and right ventricles and pumped into the systemic circulation and pulmonary circulation, respectively. ![]() The human heart is a pulsatile pump in that its function is characterized by alternating periods of contraction and relaxation. ![]()
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