Diseases caused by cytomegalovirus (CMV) and pneumonia due to pneumocytis carinii (PCP) are problematic complications after allogeneic heart transplantation. Recipients of CMV-seropositive donors have a higher morbidity of CMV. By using an anti-CMV-immunoglobulin preparation in routine prophylaxis the incidence of CMV disease after heart transplantation could be reduced significantly. Ganciclovir 10 mg/kg is administered for treatment of CMV disease for at least 14 days. Recent investigations show that a prophylactic administration of ganciclovir after heart transplantation is safe, and it reduces the incidence of CMV-induced illness in CMV-seropositive patients. The incidence of PCP after heart transplantation varies according to the literature between 1 and 13%. The onset of the disease is located mostly between the third and the fifth month after heart transplantation. An effective prophylaxis can be achieved by low dose cotrimoxazole (960 mg at two days per week in adults) within the first six postoperative months. Cases of PCP are treated by cotrimoxazole or pentamidine and are associated with a mortality up to 60%.