Effects of Combination of Bosentan and Sildenafil Versus Sildenafil Monotherapy on Morbidity and Mortality in Symptomatic Patients With Pulmonary Arterial Hypertension - A Multicenter, Double-blind, Randomized, Placebo-controlled, Parallel Group, Prospective, Event Driven Phase IV Study

COMPASS-2 is a Phase 4, prospective, randomized, double-blind, placebo-controlled, event-driven study evaluating the effect of bosentan on the time to first confirmed morbidity/mortality event in patients with symptomatic PAH already receiving sildenafil therapy. Patients must have been receiving doses of sildenafil equal to or greater than 20 mg t.i.d. for at least 12 weeks prior to being randomized. The study continued until the predefined target number of morbidity/mortality events was reached.