Pulmonary atresia with intact ventricular septum (PA:IVS) in infants is usually associated with a hypoplastic right ventricle. However, cases with enlarged right ventricle and atrium have been described with unusual frequency in prenatal series. Although these series are small, it is possible that the discrepancy with the pediatric literature is due to the very high perinatal loss rate that is found in "dilated" cases. Enlargement of the ventricle and atrium is probably the consequence of tricuspid insufficiency. Prenatal diagnosis of PA:IVS relies on the demonstration of a small pulmonary artery with an atretic pulmonary valve. The considerations previously formulated for the diagnosis of hypoplastic left heart syndrome apply to PA:IVS as well.