In addition to being effective vasodilators, angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) exert neurohumoral inhibitory actions, such as the inhibition of vascular remodeling and smooth muscle cell proliferation and the amelioration of endothelial dysfunction. These beneficial effects, render those agents appropriate for use in the treatment of pulmonary hypertension. However, data regarding the use of ACEIs or ARBs in the treatment of PHT are limited. In this study, efficacy of an ARB, losartan was compared with those of the calcium channel blocker, nifedipine in the treatment of pulmonary hypertension using echocardiographic, 6-minute walk test (6MWT), cardiopulmonary exercise test, and endothelin-1 levels.Losartan is as effective as nifedipine for reducing Doppler echocardiographically measured PAP and improving exercise capacity on 6MWT and CPET. However the short-term use of losartan or nifedipine had no statistically significant effect on endothelin-1 levels in patients with PHT.