BACKGROUND: Although patients with primary pulmonary hypertension and patients with chronic thromboembolic pulmonary hypertension with distal lesions may share similar pathophysiological characteristics, scarce information is available on the usefulness of epoprostenol in this form of secondary pulmonary hypertension. The aim of this study was to evaluate the feasibility, safety and efficacy of epoprostenol therapy in surgically untreatable patients with chronic thromboembolic pulmonary hypertension. METHODS: Continuous infusive therapy with epoprostenol was undertaken in 16 patients with primary pulmonary hypertension and in 11 surgically untreatable thromboembolic pulmonary hypertension patients. The median follow-up was 12.4 months (range 6-23 months). Patients underwent clinical, echocardiographic and hemodynamic evaluation at baseline and a 6-min walk test every 3 months after beginning epoprostenol; ultrasound evaluations were repeated in a subgroup of patients. RESULTS: Epoprostenol therapy improved the clinical status, exercise tolerance and NYHA functional class. A greater left ventricular end-diastolic volume was recorded at echocardiography in both groups. CONCLUSIONS: Epoprostenol therapy may be feasible, safe and clinically effective in patients with surgically untreatable chronic thromboembolic pulmonary hypertension.