Valsartan for Pulmonary Arterial Hypertension

Inclusion Criteria: 1. Male or female, age 18 to 80 2. WHO Group 1 Pulmonary Arterial Hypertension 3. NYHA Functional Class II, III, or IV at screening (Appendix 2 for Functional Class Decision Aid) 4. Right heart catheterization within five years demonstrating a mean pulmonary arterial pressure of ≥25 mmHg, occlusion pressure of ≤15 mmHg, and resistance ≥ 3 wood units 5. Participants with a right heart catheterization within five years demonstrating a mean pulmonary arterial pressure of ≥ 25 mmHg and occlusion pressure of 15 - 20 mmHg will be considered for inclusion if the pulmonary vascular resistance ≥ 9 wood units and they are being treated with pulmonary arterial hypertension specific therapy 6. Able to walk with/without a walking aid for a distance of at least 50 meters Exclusion Criteria: 1. Pregnant or lactating 2. Non-group 1 pulmonary hypertension or veno-occlusive disease 3. History of interstitial lung disease, unless subject has collagen vascular disease and has pulmonary function testing conducted within 12 months demonstrating a total lung capacity or vital capacity of ≥ 60 % 4. Has received or will receive an investigational drug, device, or study within 30 days or during the course of study 5. ACE-inhibitor, ARB or ARNI use within 30 days of randomization. 6. Left sided myocardial disease as evidenced by left ventricular ejection fraction \< 40% 7. Any other clinically significant illness or abnormal laboratory values (measured during the Screening period) that, in the opinion of the Investigator, might put the subject at risk of harm during the study or might adversely affect the interpretation of the study data 8. Anticipated survival less than 1 year due to concomitant disease 9. Allergy or angioedema with ACE-inhibitor use 10. Potassium \>5mEq/L or sCr \>2mg/dL at screening 11. SBP \<90mmHg at screening