A Phase 2, Double-Blind, Placebo-Controlled, Randomized Study to Compare the Efficacy and Safety of Sotatercept (ACE-011) Versus Placebo When Added to Standard of Care for the Treatment of Pulmonary Arterial Hypertension (PAH)

• Age ≥18 years

• Documented diagnostic right heart catheterization (RHC) at any time prior to Screening confirming diagnosis of WHO diagnostic pulmonary hypertension Group I: PAH in any of the following subtypes:

• i. Idiopathic ii. Heritable PAH iii. Drug- or toxin-induced PAH iv. PAH associated with connective tissue disease v. PAH associated with simple, congenital systemic-to-pulmonary shunts at least 1 year following shunt repair

• Symptomatic pulmonary hypertension classified as WHO functional class II or III

• Screening RHC documenting a minimum PVR of ≥400 dyn·sec/cm5 (5 Wood units)

• Pulmonary function tests (PFTs) within 6 months prior to Screening as follows:

‣ Total lung capacity (TLC) \>70% predicted; or if between 60 to 70% predicted, or not possible to be determined, confirmatory high-resolution computed tomography (CT) indicating no more than mild interstitial lung disease (ILD), per investigator interpretation, or

⁃ Forced expiratory volume (first second) (FEV1)/ forced vital capacity (FVC) \>70% predicted

• Ventilation-perfusion (VQ) scan (or, if unavailable a negative CT pulmonary angiogram \[CTPA\] result, or pulmonary angiography result), any time prior to Screening Visit or conducted during the Screening Period, with normal or low probability result),

• No contraindication per investigator for RHC during the study

• 6MWD ≥150 and ≤550 meters repeated twice at Screening and both values within 15% of each other, calculated from the highest value

• PAH therapy at stable (per investigator) dose levels of SOC therapies