Causes

Pulmonary valve stenosis is most often a congenital heart defect. The exact cause is unclear. The pulmonary valve doesn't develop properly as the baby is growing in the womb.

The pulmonary valve is made of three thin pieces of tissue called flaps (cusps). The cusps open and close with each heartbeat and make sure blood moves in the right direction.

In pulmonary valve stenosis, one or more of the cusps may be stiff or thick, or the cusps may be joined (fused) together. As a result, the valve doesn't open fully. The smaller valve opening makes it harder for blood to flow out of the lower right heart chamber (right ventricle). Pressure increases inside the right ventricle as it tries to push blood through the smaller opening. The increased pressure creates a strain on the heart that eventually causes the right ventricle's muscular wall to thicken.