Trial of Iloprost Inhaled Solution as Add-On Therapy With Bosentan in Subjects With Pulmonary Arterial Hypertension (PAH)

Inclusion Criteria: * Diagnosis of PAH due to PPH, connective tissue disease, HIV, or repaired (≥ 1 year) ASD, VSD, or PDA * NYHA Functional Class III or IV * On bosentan for at least 16 weeks, with the dose stable (maximum dose 125 mg BID) for at least 8 weeks * Age 12-75 years, of either gender * Six minute walk distance 100-425 meters at Baseline Exclusion Criteria: * Any new long-term treatment for PAH added within the last 4 weeks * Any therapy with a PDE (phosphodiesterase), L -arginine or a prostaglandin, concurrently, or within the last 4 weeks * PAH related to chronic thromboembolic disease, portopulmonary disease, or any etiology other than PPH, connective tissue disease, HIV, or repaired ASD, VSD, or PDA