The therapeutic effects of phosphodiesterase type 5 inhibitors in patients with pulmonary arterial hypertension (PAH) were reviewed. A double-blind, placebo-controlled study named SUPER-1 showed that sildenafil improved exercise capacity, WHO functional class, hemodynamics, and quality of life. Two randomized, double-blind, crossover studies, showed that sildenafil improved exercise tolerance and quality of life, and reduced estimated pulmonary artery systolic pressure. The dose independent effects of sildenafil on PAH are controversial. There are few case-reports that show vardenafil and tadalafil have benefits in PAH patients. A double-blind study of tadalafil in PAH patients is ongoing.