Two patients who developed posttransplant lymphoproliferative disorder with plasmacytoid changes in the lymphocytes after heart transplant are described. The first case is one of multiple myeloma, and the second is a case of lymphoma with plasmacytoid features. The clinical course and the etiologic role of the immunosuppressive therapies that the patients received for heart transplantation are described. A review of posttransplant multiple myeloma and discussion of the etiology and prognosis of this entity are presented.