Echocardiography was used in 40 patients with atrial septal defect (ASD), diagnosed by cardiac catheterization. A dilated right ventricle and abnormal interventricular septal motion were observed at M-mode echocardiography in patients with large L-R shunt. The two-dimensional apical four chamber view was reliable to detect the ostium primum type but not the secundum type of ASD. Moreover the presence of false positives reduced the specificity and predictivity of this approach. The two-dimensional subcostal view provided a direct visualization of the interatrial communication (sensitivity, specificity and predictivity = 100%) and whether the defect was in the uppermost, lowermost or midportion of the septum. Subcostal two-dimensional echocardiography is considered valuable and reliable technique to detect atrial septal defect and the type of the defect itself.