Principal Findings:

There was no between group difference in average age (52 years), weight (72 kilograms), gender (67% female), calcium channel blocker therapy (50%), NYHA class (40% class IV), the Dyspnea Index, or average 6-min walk distance of about 325 meters), mean pulmonary artery pressure of 53 mm Hg, right atrial pressure of 9 mm Hg, CO of 3.8 Liters / min, pulmonary vascular resistance of 12.9 Wood units, arterial 02 saturation (92%) and mixed venous 02 satruation (60%). 91% of patients received 5 micrograms per inhalation with an average dose of 30 micrograms per day. A combined clinical endpoint of a 10% improvement in the 6-meter walk and better NYHA class was met by 16.8% of the iloprost group compared to 4.9% of placebo, p=0.007, but the percentage who increased the distance by at least 10% did not differ. The 6-meter walk distance increased by 36.4 meters and 58.8 meters in those with primary pulmonary hypertension. 4% of the iloprost and 13.7% of placebo did not complete the study (p = 0.024), the most common reason being clinical deterioration. Hemodynamic parameters deteriorated in the placebo group after 12 weeks, and remained largely unchanged among iloprost patients. At 12 weeks the acute hemodynamic response to iloprost was equivalent in the placebo and iloprost groups. Compared to placebo, iloprost was associated with a significant improvement in NYHA, dyspnea, and quality of life. Iloprost was associated with flushing as the other prostanoids, but there were no serious side effects.