a) Pulmonary Stenosis. This
anomaly also has two forms: (i) pulmo-
nary valvular stenosis, and (ii) infundibular stenosis. In the pulmonary valvular stenosis the cups of the pulmonary valve are partially fused together to form a dome which has a central perforation. The infundibular stenosis is caused by an underdevelopment of the infundibulum (conus arteriosus) of the right ventricle. Depending on the degree of obstruction to blood flow, pulmonary stenosis is accompanied by a variable degree of hypertrophy of the right ventricle.
b) Pulmonary Atresia. In this malformation there is no orifice at the level of pulmonary valve. Consequently, the blood from right side of the heart passes to the left through a patent foramen ovale. In addition, a patent ductus arteriosus allows the blood to pass from the arch of aorta to the pulmonary trunk (which conveys this blood to the lungs). ..,