Pulmonary valve

Function

Three semilunar cusps — right, left and anterior — form the pulmonary valve, the outflow gate of the right ventricle. Unlike the atrioventricular valves it needs no chordae: the cusps' cupped shape catches backflowing blood like parachutes, snapping shut at the end of systole to create S2's pulmonary component.

Each cusp carries a small central nodule (of Morgagni) where the closed cusps meet, sealing against a diastolic pulmonary pressure of only ~10 mmHg.

Blood supply

Leaflets are largely avascular (nourished by diffusion); the surrounding infundibulum is supplied by conus branches of the coronary arteries.

Nerve supply

Passive hydraulic closure.

Clinical relevance

Pulmonary stenosis

Congenital fusion of cusps forces the right ventricle to hypertrophy — a crescendo-decrescendo murmur in the second left intercostal space.

Pulmonary regurgitation

Diastolic backflow in pulmonary hypertension produces the classic Graham Steell murmur.