Pulmonary valve

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The pulmonary valve, also called the pulmonic valve, is one of the heart’s four valves. It sits between the right ventricle and the pulmonary artery and has three cusps. It is one of the two semilunar valves, the other being the aortic valve.

How it works:
- The valve opens during right ventricular systole (when the right ventricle pressure rises above the pulmonary artery pressure) to let blood flow into the pulmonary artery.
- It closes at the end of systole as the right ventricle pressure falls, helping prevent backflow. Its closure contributes to the P2 part of the second heart sound (S2).

Location and structure:
- The pulmonary opening is roughly horizontal and lies higher than the aortic opening.
- The three cusps are named anterior, posterior, and septal (names come from fetal development).
- The edge of each cusp has a central fibrous nodule with two thin sides called the lunules.
- Each cusp forms a small pocket, the pulmonary sinus, at the start of the pulmonary trunk.

Other notes:
- The right side of the heart operates at a lower pressure, so P2 is usually softer than A2. In some healthy young people, P2 and A2 can be heard as separate sounds during inhalation.