Two children with hypoplasia of the myocardium of the right ventricle are reported. One, a girl, died at the age of 17 months, and the necropsy findings are described. In the other, a boy now 15 years of age, who was first seen at the age of 1 month, the diagnosis was made by means of cardiac catheterization, cineangiocardiography, and intracardiac electrocardiography.