In a prospective, multi-centre, randomized, double-blind, placebo-controlled study (BREATHE-5), patients with pulmonary arterial hypertension WHO functional Class III and Eisenmenger physiology associated with congenital heart disease received Tracleer 62.5 mg bid for 4 weeks, then 125 mg b.i.d. for a further 12 weeks (n = 37), or placebo (n = 17).