Seven consecutive patients with Eisenmenber's syndrome, cared for by the obstetric team in conjunction with the cardiology service, were reviewed to assess the possible role of prophylactic heparin therapy and intensive care on the outcome of these patients. In each patient, the diagnosis of Eisenmenger's syndrome was established by the demonstration of equal pulmonary arterial and aortic pressures with a predominantly right-to-left shunt at cardiac catheterization. Five of the seven patients died as follows: Three patients died between the fifth and eighth post-partum days, one patient died during the twenty-sixth week of pregnancy, and one patient died on the fifth postoperative day following tubal ligation. All of these five patients received prophylactic heparin therapy. In three patients, heparin therapy was complicated by excessive bleeding during the postoperative or postpartum period. Autopsy examination in two patients revealed no evidence of thrombosis in the main pulmonary arteries and no pulmonary infarction, contrary to the antemortem clinical suspicion. The two survivors did not receive prophylactic heparin. They comprised one patient who had normal delivery and one patient who underwent tubal ligation and induction of abortion. We conclude that the prohibitive mortality rate of Eisenmenger's syndrome during pregnancy, puerpurium, or surgical procedures probably cannot be modified with prophylactic heparin therapy. Anticoagulant treatment does not prevent deterioration of patients and probably compounds the problem by causing significant bleeding.