Experimental data suggest that transplantation of endothelial progenitor cells (EPCs) attenuates monocrotaline-induced pulmonary hypertension in rats and dogs. In addition, clinical studies suggest that autogolous progenitor cells transplantation is feasible and safe in patients with ischemic disease. This study will investigate the feasibility, safety, and initial clinical outcome of intravenous infusion of autologous EPCs in patients with idiopathic pulmonary arterial hypertension.