Myocarditis is not an uncommon finding in autopsy series of patients with AIDS, although clinically important myocarditis is rarely noted. We describe a 50-year-old woman with AIDS and chronic chagasic megaesophagus, without previous cardiac abnormalities, who experienced reactivation of Chagas' disease, characterized by the finding of Trypanosoma cruzi via direct microscopic examination of the buffy coat, xenodiagnosis, and blood culture; she developed fatal acute myocarditis. Reactivation of Chagas' disease in patients with AIDS has been reported, but in the great majority of cases it has been associated with central nervous system involvement. In areas where Chagas' disease is endemic, reactivation may occur in patients with AIDS.