At the children's hospital of Michigan a collection has been made of roentgenograms of the chest of infants and children dying from congenital cardiovascular malformations, on whom a careful postmortem examination has been performed. In reviewing groups of these cases in an effort to find more accurate criteria for antemortem diagnosis, a high incidence of atelectasis and emphysema in the lungs was observed in the group with interatrial septal defects. Our purpose here is to study this observation in detail and to test its validity by examining other comparable groups of cardiovascular abnormalities for similar manifestations. Material The material consists of 7 cases of interatrial septal defect, 10 cases of combined interatrial and interventricular septal defects, 9 cases of interventricular septal defect, and a control group of 18 cases of transposition of the great vessels. The septal defects are listed below, indicating the various types encountered and the number of each. Table I gives the relative incidence of pulmonary atelectasis and∕or emphysema in these various groups as compared with the control group, in which the principal cardiac malformation was a transposition of the great vessels. It is evident that there is a high incidence of pulmonary atelectasis and emphysema in infants dying with intracardiac septal defects, particularly with interatrial septal defects. The atelectasis tends to involve the upper lung, and the emphysema occurs predominantly in the lower lung. Eighty-six per cent of the patients with interatrial septal defects exhibited associated pulmonary atelectasis and∕or emphysema, while those with combined interatrial and interventricular defects showed an incidence of 50 per cent. Twenty-two per cent of the patients with isolated interventricular lesions had such pulmonary changes. In only 1, or 5.5 per cent of 18 patients constituting the control group with transposition of the great vessels did recognizable emphysema develop. It would seem that the frequent occurrence of atelectasis and emphysema with congenital septal defects should be of some diagnostic significance. Taussig (15) has stated that pulmonary infections occur with sufficient frequency in patients with septal defects to be of diagnostic aid. Furthermore, the fatal outcome of the cases presented in this study imparts prognostic significance to these changes. Do these manifestations represent a basic structural abnormality of the bronchi or lungs which predisposes to respiratory infection? Does the disturbance of the pulmonary circulation (dilatation of the pulmonary artery and capillaries) associated with the septal defect produce at inadequate pulmonary function which predisposes to infection, emphysema, and atelectasis? Are these infants otherwise peculiarly susceptible to respiratory infections which result in these pulmonary changes?