Infectious mononucleosis and fatal myocarditis.

Mycocarditis is an uncommon manifestation and, very rarely, a lethal complication of infectious mononucleosis. A 14-year-old girl initially had exudative pharyngitis and splenomegaly and developed refractory ventricular fibrillation. The diagnosis of infectious mononucleosis was confirmed by both a strongly positive heterophil antibody test and a high titer of Epstein-Barr virus. Pathologic studies demonstrated extensive histiocytic and lypmhocytic infiltration of the myocardium.