Lipomas of the heart are rare (only 0.5% according to the Armed Forces Institute of Pathology series) and their diagnosis is often difficult because they are asymptomatic; in fact, in contrast to lipomatous hypertrophy, lipomas are usually found on the epicardial surfaces of the atria or ventricles. In our case, the lipoma was located in both atria and was attached to the interatrial septum involving also the right pulmonary veins, the inferior vena cava and the right phrenic nerve. At histology, the tumor was composed only of mature adipose tissue with entrapped myocytes and vessels. The combination of computed tomography and transesophageal echocardiography allowed a precise diagnosis in terms of the localization and tissue characterization of the tumor.