Lipomatous hypertrophy of the interatrial septum (LHIS) is a rare benign entity characterized by the excessive fat deposition in the interatrial septum with typical sparing of the fossa ovalis. We report a case of a 61-year-old woman with an incidentally found LHIS associated with fatty replacement of the ventricular myocardium and epicardial mediastinal lipomatosis diagnosed by computed tomography (CT) and MRI.