Few chroniclers of heart disease have stressed the importance of aortic-valve atresia as a congential defect. However, at the Hospital for Sick Children, Toronto, this lesion is the most frequent cause of congestive heart failure and death in the neonatal period. In the cases presented, the average survival was 4 1/2 days, with a maximum survival of 7 1/2 months. The chief clinical features were cyanosis, dyspnea, rapidly progressive heart failure with hepatomegally, and often a gallop rhythm. Pulmonary ejection murmurs and weak peripheral pulses were both frequently noted. The x-rays showed cardiomegally with pulmonary congestion. The electrocardiogram indicated right atrial and right ventricular hypertrophy. The prognosis is at present hopeless, but it is desirable to differentiate this condition from the more easily remediable causes of neonatal distress.