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Why do semilunar valves not need chordae tendineae?

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Illustration of a human heart cross-section showing four chambers-left and right atria and ventricles-with labeled major blood vessels. An inset highlights cardiac muscle tissue, showing myocytes and intercalated disks. — human cardiovascular system The human heart is both a pump and a muscle. Its four chambers move blood efficiently, while cardiac muscle cells joined by intercalated disks synchronize each contraction.

Semilunar valves do not require chordae tendineae because of their unique pocketlike structure. Unlike atrioventricular valves, which are leaflike flaps that require tethering to prevent them from billowing backward into the atria under high pressure, semilunar valves are shaped like half-moons.12

When blood flows from the ventricles into the aorta or pulmonary artery, the pressure pushes these pocketlike cusps against the walls of the vessels, allowing blood to pass. When the ventricles relax and pressure in the arteries exceeds that in the ventricles, blood flows back toward the heart and fills these pockets. This filling causes the cusps to expand and meet in the center, effectively sealing the orifice and preventing backflow without the need for additional structural support like chordae tendineae or papillary muscles.12