Which valves prevent backflow of blood into the ventricles during ejection?

The semilunar valves are the structures responsible for preventing backflow of blood into the ventricles during the ejection phase of the cardiac cycle. These valves are located between the ventricles and their respective arteries—the aorta for the left ventricle and the pulmonary artery for the right ventricle.

When the ventricles contract to pump blood out of the heart, the pressure generated forces the semilunar valves to open. Once the ventricles have finished contracting and begin to relax, the pressure in the arteries becomes greater than the pressure in the ventricles. This change in pressure causes the semilunar valves to close, effectively preventing any blood that has been ejected into the arteries from flowing back into the ventricles. This mechanism ensures that blood moves in one direction, maintaining efficient circulation.

The atrioventricular valves, which include the mitral and tricuspid valves, serve a different purpose—they prevent backflow of blood from the ventricles into the atria during ventricular contraction. The coronary valves do not exist as a distinct type of valve in the heart's anatomy, and the tricuspid valve is one of the atrioventricular valves rather than a semilunar valve. Thus, the key role of the sem