• Change from baseline in exercise capacity, as measured by distance walked in six minutes (6-Minute Walk test). [ Time Frame: Week 12 ] [ Designated as safety issue: No ]
  

• Change from baseline in mean pulmonary arterial pressure [ Time Frame: Week 12 ] [ Designated as safety issue: No ]
  
• Time from randomisation to the first occurrence of clinical worsening (death or lung transplantation or hospitalisation due to pulmonary hypertension or initiation of prostacyclin therapy or initiation of bosentan therapy) [ Time Frame: Week 0 to 12 ] [ Designated as safety issue: No ]
  
• Change from baseline in the BORG dyspnoea score [ Time Frame: Week 12 ] [ Designated as safety issue: No ]
  
• Change from baseline in pulmonary hypertension criteria for functional capacity and therapeutic class [ Time Frame: Week 12 ] [ Designated as safety issue: No ]
  
• Change from baseline in the 8 dimensions of SF-36 (Physical functioning, Role functioning, Bodily pain, General health, Vitality, Social functioning, Mental health and Reported health transition) [ Time Frame: Week 4 and Week 12 ] [ Designated as safety issue: No ]
  
• Change from baseline at Weeks 4 and 12 in the 5 dimensions of ED5Q (Mobility, Self care, Usual Activities, Pain/Discomfort and Anxiety/Depression) [ Time Frame: Week 4 and Week 12 ] [ Designated as safety issue: No ]
  
• Patient overall preference assessment [ Time Frame: Week 12 ] [ Designated as safety issue: No ]
  
• Change in Chronic Use of Background Therapy for Pulmonary Arterial Hypertension [ Time Frame: throughout the study ] [ Designated as safety issue: No ]
  
• Change from baseline in hemodynamic parameters [ Time Frame: Week 12 ] [ Designated as safety issue: No ]
  

Inclusion Criteria:

Included patients had primary pulmonary arterial hypertension, pulmonary hypertension secondary to connective tissue disease, or pulmonary hypertension with surgical repair at least 5 years previously; a mean pulmonary artery pressure greater than or equal to 25 mmHg and a pulmonary artery wedge pressure of less than or equal to 15 mmHg at rest, via right heart catheterisation within 21 days prior to randomisation; and a baseline 6-Minute Walk test distance of 100 m to 450 m.

Exclusion Criteria:

Subjects with congenital heart disease, pulmonary hypertension due to thromboembolism, HIV, chronic obstructive airway disease, congestive heart failure or schistosomiasis; subjects with significant (ie > 2+) valvular disease other than tricuspid regurgitation or pulmonary regurgitation; and acutely decompensated heart failure within the previous 30 days; subjects with pulmonary hypertension secondary to any other etiology other than those specified in the inclusion criteria.