Lipomatous Hypertrophy of the Interatrial Septum Manifesting as Third Degree Atrioventricular Block.

A 55-year-old patient was found to have complete heart block during preoperative assessment. Cardiac magnetic resonance imaging revealed an interatrial mass suggestive of primary cardiac tumor. Extensive evaluation including intracardiac biopsy and finally open resection revealed lipomatous hypertrophy masquerading as tumor. (Level of Difficulty: Intermediate.).