• Primary Outcomes: Change in distance traversed during the six minute walk test at 8 weeks;
  
• Adverse events
  

• Secondary Outcomes: Borg dyspnea score immediately after the six minute walk test;
  
• WHO functional classification;
  
• Symptoms of PAH;
  
• Specific prostacyclin side effects;
  
• Total weekly time spent with specific activities associated with intravenous Remodulin therapy compared to the total weekly time spent on specific activities with inhaled Ventavis;
  
• Score on treatment satisfaction scale;
  
• Score on quality of life questionnaire
  

Pulmonary arterial hypertension (PAH), which is defined as an elevation in pulmonary arterial pressure and pulmonary vascular resistance, is a severe hemodynamic abnormality common to a variety of diseases and syndromes. Elevation in pulmonary arterial pressure causes an increase in right ventricular afterload, impairing right ventricular function and ultimately leading to inactivity and death. The goal of PAH treatment is to lengthen survival time, to ameliorate symptoms of PAH and to improve quality of life (QOL).

Remodulin (treprostinil sodium), a prostacyclin analog, possesses potent pulmonary and systemic vasodilatory and platelet anti-aggregatory actions in vitro and in vivo. Remodulin is an approved pharmacotherapy for PAH delivered as either a continuous subcutaneous infusion or intravenous infusion.

Ventavis (iloprost)is an inhaled prostacyclin analogue with similar properties to Remodulin. In December 2004, Ventavis was approved for use in the United States by the FDA for the treatment of pulmonary arterial hypertension (WHO Group I) for patients with NYHA III or IV symptoms.

As the PAH community gains experience with the use of inhaled Ventavis, questions have arisen as to how to transition a patient on inhaled Ventavis to Remodulin in the presence of worsening symptoms or at a patient's request related to dissatisfaction with the frequency of daily treatments. This study will examine effects of switching from Ventavis to IV Remodulin and compare changes in exercise capacity, safety, HRQOL and treatment satisfactions.

Participation will last up to 12 weeks. Study procedures include routine blood tests, medical history, physical exams, disease evaluation, exercise tests and patient questionnaires. Participates will have 4 clinic visits during the study and will spend at least one night in the hospital.