Assess the Efficacy and Safety of Sildenafil When Added to Bosentan in the Treatment of Pulmonary Arterial Hypertension

A Multinational, Multicentre, Randomized, Double-blind Study To Assess The Efficacy And Safety Of Oral Sildenafil 20mg Tid Or Placebo When Added To Bosentan In The Treatment Of Subjects, Aged 18 Years And Above, With Pulmonary Arterial Hypertension (Pah)

To assess the efficacy and safety of sildenafil when added to patients with PAH who are taking bosentan as all or part of their background therapy.

Inclusion Criteria:

• Subjects aged 18 and over above with PAH and for which bosentan therapy is indicated according to national license
• Subjects with a mean pulmonary artery pressure of >25mmHg and a pulmonary artery wedge pressure of <15mmHg at rest via right heart catheterization within 3 years prior to randomization.
• Subjects whose baseline 6 Minute Walk Test distance is >100m and < 450m.

Exclusion Criteria:

• PAH secondary to any aetiology including congenital heart disease other than those specified in the inclusion criteria
• Subjects whose 6 Minute Walk Test may be limited by conditions other than PAH related dyspnoea or fatigue eg. claudication from vascular insufficiency or arthritis.