Clinical Trial to Evaluate the Long-term Safety of Udenafil in Patient With PAH

Pulmonary arterial Hypertension is characterized by a progressive incerease in pulmonary vascular resistance(PVR) leading to right ventricualar failure. Udenafil inhibits PDE 5, an enzyme that metabolizes cGMP, enhancing the cGMP mediated relaxation and growth inhibition of vascular smooth muscle cells, including those in the lung.