Lipomatous hypertrophy of the interatrial septum is an uncommon entity that usually occurs in elderly patients. We report a patient who presented with atrial fibrillation, congestive cardiac failure and a large intracavitary mass in the right atrium on echocardiography. He underwent successful resection of the mass with septal reconstruction. Pathology was consistent with lipomatous hypertrophy of the interatrial septum.