129 Xenon Imaging in Patients Treated With Sotatercept

This study uses a special type of MRI scan with inhaled xenon gas — a safe and non-radioactive imaging technique — to see how well the lungs and blood vessels are functioning in patients being treated with sotatercept, a drug approved for pulmonary arterial hypertension (dangerously high blood pressure in the lungs). **You may be eligible if...** - You are between 18 and 75 years old - You have been diagnosed with pulmonary arterial hypertension (PAH, Group 1) confirmed by right heart catheterization - You have been on a stable dose of PAH medication for at least 90 days before enrolling - Women of childbearing potential must have a negative pregnancy test **You may NOT be eligible if...** - You have moderate to severe heart disease (such as poor heart pumping function or serious valve disease) - You have chronic blood clots in the lung (chronic thromboembolic disease) - You cannot safely undergo MRI (e.g., metal implants) - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.