Toxoplasma gondii infections in heart transplant recipients are generally seen as acquired infections of the immunocompromised sero-negative patient from an exogenous source, usually the donor organ. We report a 19-year-old heart transplant recipient who developed a collapse of heart functions, 28 days after the transplantation. Histopathological examination of the endomyocardial biopsy revealed T. gondii infection. After the appropriate medical therapy regimen, the patient’s ejection fraction recovered dramatically. The control endomyocardial biopsy of the patient revealed any histopathologic sign of T. gondii infection or acute rejection. In both preoperative and postoperative serologic tests of the recipient, T. gondii IgG values were negative. Although a seroconversion of T. gondii IgG/M was not detected, a twofold rise was significant in the titer of IgG. Unfortunately the serologic status of the donor was not known, but the recipient of liver of the same donor is known to have an infection-free course. However, the heart transplant recipient died on the 65th day of transplantation because of other reasons. Our case demonstrates that the histological diagnosis of T. gondii is precious for recovery. In conclusion, T. gondii infection should be kept in mind while interpreting endomyocardial biopsies of transplanted heart. It is significant to distinguish its histopathologic symptoms from a possible rejection because the therapies of these two entities are completely different and depends on the pathological diagnosis.