The pathology of pulmonary arterial hypertension (PAH) is characterized by vascular vasoconstriction, smooth muscle cell proliferation, and thrombosis. Experimental studies have shown the beneficial effect of phosphodiesterase type 5 (PDE-5) inhibitors on pulmonary vascular remodeling and vasodilatation. Randomized clinical trials in monotherapy or combination therapy have been conducted in PAH with sildenafil and tadalafil which significantly improve clinical status, exercise capacity and hemodynamics of PAH patients. Combination therapy of PDE-5 inhibitors with prostacyclin analogs and endothelin receptor antagonists may be helpful in management of PAH. The third PDE-5 inhibitor, vardenafil, is currently being investigated in PAH. Side effects are usually mild and transient and include headache, flushing, nasal congestion, digestive disorders, and myalgia.