The purpose of this study is to see if the drug sotatercept given for 36 weeks improves the functioning of the heart and improves quality of life.

Inclusion Criteria

• Informed consent obtained before any trial-related activities. Trial-related activities are any procedures that are carried out as part of the trial, including activities to determine suitability for the trial.
• NYHA Class II-IV.
• LVEF ≥ 40 % within the preceding year.
• No recent initiation of pulmonary vasodilator in the last 60 days.
• Pulmonary arterial hypertension by right heart catheterization (Mean PA pressure ≥ 20 mmHg with PVR>2 Wood units) with no evidence of heart failure with preserved ejection fraction (exercise PCWP <25 mm Hg).
• Symptomatic PAH patients with plan to undergo exercise RHC for reassessment of exertional symptoms.

Exclusion Criteria

• Myocardial infarction, stroke, hospitalization for heart failure, unstable angina pectoris or transient ischemic attack within 30 days prior to the day of screening.
• Planned coronary, carotid, or peripheral artery revascularization.
• Any other condition judged by the investigator to be the primary cause of dyspnea (such as heart failure due to restrictive cardiomyopathy or infiltrative conditions (e.g., amyloidosis), hypertrophic obstructive cardiomyopathy, anemia, or more than moderate mitral or aortic heart valve disease).
• Wheelchair bound or orthopedic inability to exercise.
• Chronic hypoxemia with inability to exercise without oxygen supplementation.
• Skeletal muscle myopathy.
• History of rhabdomyolysis.
• Participation in any clinical trial of an approved or non-approved device for the treatment of pulmonary hypertension within 30 days before screening.
• Receipt of any investigational medicinal product within 30 days before screening.
• Female who is pregnant, breast-feeding or intends to become pregnant or is of child-bearing potential and not using a highly effective contraceptive method.
• Major surgery scheduled for the duration of the trial, affecting walking ability in the opinion of the investigator.
• Any disorder, including severe psychiatric disorder, suicidal behavior within 90 days before screening, and suspected drug abuse, which in the investigator´s opinion might jeopardize subject´s safety or compliance with the protocol.