The atrial septum can be visualized by right sternal border 2-dimensional echocardiography (2-D echo). To evaluate the usefulness of this approach in the evaluation of atrial septal defect (ASD), 50 patients who underwent cardiac catheterization were studied by 2-D echo. Twenty-one patients (Group A) had ASD (3 ostium primum, 18 ostium secundum) and 29 (Group B) had mitral valve disease and an intact atrial septum. Subcostal and right sternal border approaches were used to visualize the atrial septum. Both approaches identified the 3 cases of ostium primum ASD; secundum ASD was identified using the subcostal approach in 11 patients and using the right sternal border approach in 13. In 15 patients the ASD was imaged at least by 1 of the 2 approaches. Two-dimensional contrast echocardiography showed a positive or negative contrast effect in 13 of 18 cases (12 with standard approaches, 11 with right sternal border approach). In all patients in Group B, the right sternal border approach showed an intact atrial septum. Thus, the right sternal border approach is a useful approach that increases the sensitivity of 2-D echo in the diagnosis of ASD.