Fifty cases of pulmonary atresia with intact ventricular septum were reviewed. The patients were divided into two groups depending on the size of the right ventricle. Clinical, roentgenographic, and electrocardiographic findings in each group are discussed. The most reliable method for determining the size of the right ventricle is selective angiography with injection of dye into the right ventricle. Up until 1967, with or without having surgery, patients of both groups died. Since then emergency cardiac catheterization and balloon septostomy followed by operative creation of a Potts' anastomosis and ligation of patent ductus arteriosus has improved results in patients with a small right ventricle.