pulmonary valve

The pulmonary valve is the exit gate from the right side of the heart toward the lungs. It is the mirror image of the aortic valve: a three-petal door that opens to let blood out and shuts to keep it from falling back.

It sits at the exit of the right ventricle into the pulmonary artery and has three semilunar cusps. When the right ventricle contracts, the valve opens and oxygen-poor blood is ejected toward the lungs; when the ventricle relaxes, the cusps close to stop backflow. Its closure contributes the second component of the second heart sound.

Because the right side of the heart works at low pressure, the pulmonary valve faces far less mechanical stress than the aortic valve and is rarely diseased in adults. When problems do occur, they are most often congenital — a narrowed valve (pulmonary stenosis) is a feature of several heart conditions present from birth.