CONGENITAL pulmonary stenosis occurs most frequently in conjunction with defect of the ventricular septum, overriding of the aorta, and hypertrophy of the right ventricle. In this syndrome, known as the tetralogy of Fallot, the stenosis practically always involves the infundibulum of the right ventricle, and the pulmonary valve may be normal. In certain instances the stenosis is valvular, but here also the infundibulum shows more or less narrowing.
There is a second type of congenital pulmonary stenosis, less frequent, but by no means rare, in which the ventricular septum is intact. Obviously, there can be no overriding of the aorta. There may, however, be a right-to-left shunt through the foramen ovale if it has remained open or has been forced open by increased pressure on the right side of the heart. The pathology in the region of the pulmonary valve offers a sharp contrast to that seen in the tetralogy