The broad aim of this investigation is to determine whether the modulating effect of angiotensin converting enzyme inhibition on vascular smooth muscle responsiveness to the nitric oxide pathway that we have observed in an animal model of Congestive Heart Failure(CHF) can be exploited in humans with PAH. Furthermore, we have identified a group of genes TAO kinase I, IL-10, Rho kinase, Raf1, bile acid coenzyme A and Fmr1 that are modulated by long-acting angiotensin-converting enzyme inhibitor (ACEI) in our animal model, and therefore may also be modulated by ACEI in patients with PAH