Twenty patients with secundum atrial septal defect, who had undergone open heart surgery were studied retrospectively. Girls were more affected than boys; the sex ratio was 1.5:1. Associated cardiac defects were diagnosed in two patients, one with moderate valvular pulmonic stenosis and the other one with small ventricular septal defect. Typical clinical findings consisted of loud first heart sound, widely fixed split second heart sound and soft ejection systolic murmur at the upper left sternal border were heard in all cases. Mid diastolic murmur due to relative tricuspid stenosis was detected in most cases (75%). Electrocardiographic findings included right axis deviation, prolonged PR-interval and right atrial enlargement were found in 50%, 15% and 60% of cases, respectively. Incomplete right bundle branch block and right ventricular enlargement were found in all cases, as was cardiomegaly with increased vascular markings were found in all cases. Paradoxical ventricular septal motion and visualization of the atrial septal defect were seen in 95% and 75% of cases, respectively. Cardiac catheterization was performed in 19 patients (95%). The pulmonary-systemic flow ratio (Qp/Qs) ranged from 1.7 to 6.3 (mean 2.9 +/- 0.67), and was correlated to the presence of mid diastolic tricuspid flow murmur and paradoxical ventricular septal motion. Simple closure of the defect was the procedure of choice, but in one patient (5%) pericardial patch was used to close the very large defect. The mortality rate was 10 per cent. Physical retardation was found in all boys and 50% of girls, before surgery. Body weight percentile increased in most cases (61.1%), while body height percentile increased in only 5.6% of cases, postoperatively. Ejection systolic murmur at the upper left sternal border was still detected in one patient (5.6%). Incomplete right bundle branch block persisted in all cases, while cardiomegaly was still found in 5.6% of cases followed-up six months to five years after surgery. There was no residual left ventricular dysfunction in all cases.