The narrowing of the pulmonary valve (white arrow in diagram) may cause the right ventricle (RV) to pump harder to move its supply of blood into the pulmonary artery (PA). This increases the blood pressure in the right ventricle and may result in the thickening (hypertrophy) of its walls.

The blood flow is turbulent in pulmonary stenosis as it passes to the pulmonary artery and therefore a murmur is always present, even with mild stenosis.

The pulmonary stenosis may interfere with the proper functioning of the right ventricle and, in extreme cases, lead to right ventricular failure. The child with Pulmonary Stenosis usually shows no symptoms. Children with severe stenosis may breathe rapidly, feed poorly, and tire easily.