Both sildenafil (21) and tadalafil (22) have been demonstrated to be effective in PAH and are FDA approved for this indication. The endothelin-receptor antagonists, bosentan (23) and ambrisentan (24), are also FDA-labeled for this indication and represent alternative options for oral therapy of PAH (25). A small randomized study comparing sildenafil with bosentan suggested that sildenafil was superior in reducing RV mass and improving exercise capacity in patients with PAH (26). Recently, the results of a large multi-center randomized, controlled trial of tadalafil therapy for PAH have been presented. The data indicate, that similar to sildenafil, tadalafil at doses of 20 and 40 mg per day, improved exercise capacity. In addition, tadalafil 40 mg per day improved pulmonary hemodynamics, quality of life and reduced the incidence of clinical worsening.