We propose to study the short-term effect of combined angiotensin converting enzyme inhibitor (ACEI) and angiotensin receptor blocking (ARB) therapy in patients with PH, in a controlled, randomized, two-year study. Primary endpoints will be urinary markers of renal tubular injury (retinol binding protein (RBP), alpha 1 microglobulin (α1m), γ-glutamyl transferase (GGT)) and interstitial fibrosis (transforming growth factor beta 1 (TGFβ1). Secondary endpoints will be the rates of change in renal tubular injury and renal function as determined by serum creatinine and creatinine clearance.