Mycobacterium marinum (M. marinum) is a species of nontuberculous mycobacteria that is a rare cause of disease in humans and is usually associated with aquatic exposures. Symptoms manifest, on average, three weeks after exposure, although cases with longer incubation periods have been reported in the literature. Herein, we describe an unusual case presentation of an M. marinum infection in the left upper extremity of a heart transplant recipient. The case is notable for its prolonged incubation period and for being the first documented case of M. marinum infection in a heart transplant recipient. We hypothesize that, given the patient's immunosuppressive medication regimen in the post-transplant period, this case could represent a reactivation phenomenon of a latent infection.