Consecutive patients transplanted between January 1984 and December 1988 were followed until August 1992 to detect fatal and nonfatal thromboembolic complications, including sudden death, acute and chronic myocardial infarction, pulmonary and peripheral embolisms, stroke, and thrombophlebitis. The probability of developing such complications was 9.86 per 100 patients per year. The probability of fatal complications was 3.97% per year; the mean interval between transplant and death was 1247 days versus 29.5 days for nonthromboembolic deaths. Thromboembolic deaths represented 5.1% of total mortality at the first year posttransplant but 57, 30, 67 and 73% at the second, third, fourth, and fifth years, respectively. Among the prognosis factors that were analyzed, none was significant predictor of thromboembolic complication. This high prevalence of thromboembolic complications suggests that effective antithrombotic strategy should be defined in heart transplant recipients.