Lipomatous hypertrophy of the interatrial septum (LHIS) is a rare lesion of unknown origin usually diagnosed as an incidental finding during autopsy. It can be associated with supraventricular arrhythmias, venous return obstruction and sudden cardiac death. Five necropsy cases (4 females, 1 male) of LHIS were encountered during the last 31 years; only one case from this series was diagnosed ante mortem. The patients’ mean age was 68 years; their mean BMI was 28.4. The mean size of the lesion was 31 mm. In three patients the LHIS was asymptomatic, two patients experienced relapsing multifocal atrial tachycardia and sick sinus syndrome, respectively. Histologically, all cases consisted of a mixture of mature and brown adipose tissue with foci of cardiomyocytes. For a pathologist the knowledge of LHIS is important because of an increasing possibility of its ante mortem diagnosis by imaging methods with a following endomyocardial biopsy, and also because it may appear as a cause of sudden cardiac death.

        Key words: heart – interatrial septum – adipose tissue – arrhythmia – lipomatous hypertrophy