An enlarged right ventricle and abnormal ventricular septal motion are characteristic echocardiographic features of atrial septal defect and often persist after the defect has been completely closed, even when the operation clinically is judged to be successful. These features were examined retrospectively 15 to 21 months after operation in a group of children whose atrial septal defect had been closed between January 1976 and July 1979. Despite satisfactory postoperative results in all, about two thirds had an enlarged right ventricular dimension and about the same number had abnormal septal motion when examined echocardiographically an average of 18 months after operation. The best operative strategy seems to be to operate while the right ventricular end-diastolic dimension is still relatively small in echocardiographic terms.