This open-label, LTFU study will evaluate the safety, tolerability, and efficacy of sotatercept in participants with PAH previously treated with sotatercept or placebo. Participants eligible to enroll in this study will have participated in and completed the relevant study participants of the parent PAH sotatercept clinical trials. The estimated duration of the A011-12 study is up to 7 years; however, the estimated duration of enrollment for each participants is approximately 4 years. There is no formal sample size calculation for the study. The number of participants in this LTFU study is dependent upon the enrollment in the parent protocols. Approximately 700 participants are anticipated to enroll in the study.

The PHAR is a multicenter, prospective registry of newly evaluated patients at PHCCs in the United States who have either PAH or CTEPH. Baseline information will be collected at the time of initial evaluation at the PHCC (within six months of the initial outpatient PHCC visit) with follow-up data collected at approximately 6-month intervals. This study will determine how patients with PH are evaluated, tested, and treated, and will observe how well patients do. The goal of the project is to see if patients with PH are treated according to recommended guidelines and to see if there are certain factors which lead to better or worse outcomes in patients with PH. There is no intervention or study medication used and there is no limitation to how a patient is treated in this study.

Patients with systemic sclerosis (SSc) related pulmonary arterial hypertension (SScPAH) have a worse prognosis than those with idiopathic PAH. We have recently discovered that heart cells in SScPAH do not contract or squeeze as well as in other forms of pulmonary hypertension. However, the mechanism leading to this dysfunction is not understood. To better study this and in hopes of developing a future therapy, we plan to collect tissue samples via a heart biopsy at the time of a clinically indicated heart catheterization.