Interatrial septal aneurysms are uncommon lesions characterized by the protrusion of the fossa ovalis region of the interatrial septum into the left or right atrium. This study consisted of 10 patients wo were transesophageal echocardiographically diagnosed as having interatrial septal aneurysms during a 20 month period. In two of six patients with atrial shunt, the QP/QS exceeded 1.5. Surgery was performed on six patients. Primary factors in the choice of therapy were the level of shunt and concomitant lesions. In conclusion, transesophageal echocardiography seems to be the most reliable method for helping clinicans arrive at an appropriate decision as to therapeutic modality.