Clinical signs of heart failure developed in two cardiac transplant recipients and were interpreted initially as graft rejection. Morphologic examination ofexplanted hearts revealed myocarditis with abscess formation and necrosisconsistent with a bacterial process; Listeria monocytogenes was isolated from myocardial tissue in the first case and from blood in both. The first patient also developed signs of meningoencephalitis, but the second had no signs of infection outside the heart. Antimicrobial therapy and retransplantation were successful in eradicating listeriosis. The differential diagnosis of heart failure in cardiac transplant recipients includes infectious myocarditis due to L. monocytogenes. © 1990 by the The University of Chicago. All rights reserved.