Posttransplantation lymphoproliferative disease (PTLD) is one of the most serious complications of chronic immunosuppression in transplant recipients. Involvement of the cardiac allograft or development of lymphoma in the heart is extremely rare. We report a primary cardiac lymphoma that developed about 14 months after the operation in a cardiac recipient. The patient presented with vague abdominal complaints. Multiorgan failure developed within a short period of time, and the patient died. The diagnosis of "diffuse large cell lymphoma of B cell type" was made on postmortem examination.