STENOSIS of the pulmonary valve is the only abnormality of note in a small but significant number of patients with cyanosis due to congenital heart disease. The pathologic process in such patients differs from that seen in typical tetralogy of Fallot in that the interventricular septum is intact and consequently there can be no overriding of the aorta. Instead of stenosis in the infundibular region as usually seen in the tetralogy of Fallot, stenosis in these cases is caused by fusion of the cusps of the pulmonary valve (fig. 2D). The degree of this fusion, varying from negligible to complete, determines the severity of the symptoms.
Immediately distal to the stenosis marked dilatation of the pulmonary artery is usually seen. It is mysterious that poststenotic dilatation of the pulmonary artery is practically always present although pressure in the pulmonary artery is low. In fact, patients with the severest pulmonary stenosis,