Lipomatous hypertrophy of the interatrial septum (LHIS) is a rare benign disorder that is characterized by accumulation and deposition of fat in the interatrial septum. Its etiology is still unknown, despite the theories that have been suggested. It usually occurs in older, obese people with a higher incidence in women. In most cases its diagnosis is made incidentally. Cardiac arrhythmias including atrial fibrillation, atrial premature contractions and atrioventricular block may occur as a consequence of involvement of the atrial wall and atrioventricular conduction pathways. We present a case of LHIS in an 87-year-old Italian woman.