To determine the relationship of cytomegalovirus infections (CMVI) to immunosuppression in heart transplants, we retrospectively compared demographic and clinical variables in 154 consecutive heart transplant patients. Forty-one CMVI were compared; of these, 30 (73%) were identified in tissue, and nine (22%) were identified by blood or urine culture. Twenty (49%) of the CMVI were self-limited, and 21 (51%) were progressive, requiring treatment. When comparing patients with and without CMVI, demographic variables, mean preexisting heart disease, cyclosporine level, cumulative corticosteroid dose, and the use of anti-T-cell antibodies were examined. Only the use of OKT3 was significantly associated with the subsequent development of CMVI. Although CMVI subsequently developed in 30 of 79 (38%) patients who had received OKT3, CMVI developed in only 11 of 75 (15%) patients who had not received OKT3 (p = 0.01). Furthermore, the incidence of CMVI increased with increasing total OKT3 dose (none, 11 of 64 [17%]; < or = 75 mg, 23 of 66 [35%]; > 75 mg, 6 of 14 [43%]; p = 0.01). Logistic regression showed that the only two variables predictive of CMVI were the use of OKT3 (p = 0.0023) and ischemic rather than idiopathic heart disease before transplantation (p = 0.0098). Rejection rates, incidence of allograft vasculopathy, and 1-year actuarial survival were not influenced by previous CMVI. Pneumocystis carinii pneumonia occurred more frequently in patients with CMVI than in those without (13 of 41 [32%] patients versus 3/113 [3%] patients; p < 0.001). No correlation existed between CMVI and lymphoproliferative disorder (p = 0.84).(ABSTRACT TRUNCATED AT 250 WORDS)