Heart Valves
The heart contains four valves that open and close allowing blood to flow in one direction. The tricuspid and bicuspid valves separate the atria from the ventricles. When these valves are closed, the atria fill with blood. When the atria contract and the valves open, the blood moves from the atria to the ventricles below. When the ventricles contract, the semilunar valves, located at the beginning of the pulmonary arteries and the aorta, open and blood is pumped out.
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