Background: Treatment of patients with secondary pulmonary hypertension has been unsatisfactory. Objective: To describe exercise capacity, functional class, and hemodynamic variables after long-term intravenous infusion of prostacyclin in patients with secondary pulmonary hypertension. Design: Case series. Setting: Academic referral center. Patients: 33 patients with secondary, precapillary pulmonary hypertension (New York Heart Association class III or IV). Intervention: Continuous intravenous prostacyclin administered by portable infusion pump on a compassionate-use basis. Measurements: Functional class, treadmill time, and hemodynamic variables. Results: Patients were followed for an average of 12.7 +/- 5.6 months. Exercise tolerance and New York Heart Association class improved in each patient. The duration of treadmill exercise increased from 186 seconds to 491 seconds, an increase of 305 seconds (95% CI, 194 to 417 seconds; P < 0.001). Mean pulmonary artery pressure decreased from 60 mm Hg to 46 mm Hg. a decrease of 14 mm Hg (Cl, 9 to 19 mm Hg; P < 0.001). Cardiac output increased from 3.90 L/min to 6.30 L/min, an increase of 2.40 L/min (CI, 1.56 to 3.25 L/min; P < 0.001). The pulmonary vascular resistance decreased from 1143 dynes . s/cm(5) to 575 dynes . s/cm(5), a decrease of 567 dynes s/cm(5) (CI, 407 to 727 dynes . s/cm(5); P < 0.001). Patients with collagen vascular disease, congenital heart disease, and portopulmonary hypertension were analyzed with other patients and separately. All groups had a statistically significant reduction in mean pulmonary artery pressure and a statistically significant increase in cardiac output. Conclusion: Intravenous prostacyclin may be effective in the treatment of patients with certain types of secondary pulmonary hypertension.