Myocarditis is an inflammatory form of heart disease which is usually preceded by a viral infection. Giant cell myocarditis is an uncommon and nonspecific form of this disease. Sporadic reports have linked giant cell myocarditis with thymoma and concomitant myositis. The authors report a patient with leprosy who, six months after initiation of treatment, developed sudden onset of congestive heart failure and cardiac arrhythmias unresponsive to aggressive medical therapy. In addition to confirming leprosy, autopsy showed a mixed cell type thymoma, severe giant cell myocarditis and extensive myositis.