Upon entering this study, your initial health status will be recorded. This includes measurements of your body weight, blood pressure, and an electrocardiogram (a test that records the electrical activity of your heart).

Blood samples will be collected to check various parameters including red blood cell count, white blood cell count, platelet count, hemoglobin (the protein in blood that carries oxygen), and hematocrit (the proportion of blood made up of red blood cells).

Additional blood tests will measure levels of substances such as blood urea, creatinine, bilirubin, liver enzymes (aspartate aminotransferase, alanine transaminase, alkaline phosphatase), minerals (sodium, potassium, chloride, calcium, phosphorous, magnesium), glucose, carbon dioxide, and albumin.

A 6-minute walk test will be performed to measure how far you can walk in six minutes.

Blood will be tested for NT-proBNP levels, a substance that indicates how well your heart is functioning.

Your functional status will be assessed using the World Health Organization Classification, which categorizes how much your condition limits your daily activities.

A measurement called pulmonary vascular resistance will be taken to assess the blood flow through the vessels in your lungs.

Your risk level will be evaluated using the Simplified French Risk Score Calculator.

You will receive sotatercept, which is administered as an injection under the skin (subcutaneous injection).

The medication is provided as a solution for injection.

Sotatercept will be given in addition to your existing treatment for pulmonary arterial hypertension (high blood pressure in the arteries of the lungs).

The specific dosage, frequency, and duration of sotatercept administration will be determined according to the study protocol and your individual response to treatment.

Throughout the study, you will attend scheduled visits to monitor your health and response to treatment.

At these visits, the same assessments performed at baseline will be repeated, including measurements of body weight, blood pressure, and electrocardiogram.

Blood samples will be collected regularly to monitor hematology parameters (blood cell counts and related measurements) and chemistry parameters (various substances in your blood).

The 6-minute walk test will be repeated to track changes in your exercise capacity.

NT-proBNP levels will be measured to monitor heart function.

Your functional status according to the World Health Organization Classification will be reassessed.

Pulmonary vascular resistance measurements will be repeated.

Your risk level using the Simplified French Risk Score Calculator will be reevaluated.

Any side effects or health changes you experience will be recorded and assessed.

Blood samples will be collected at specified times to check for the presence of anti-drug antibodies.

Anti-drug antibodies are proteins your immune system may produce in response to the study medication.

This is a long-term study designed to evaluate the safety and effects of sotatercept over an extended period.

You will continue to receive sotatercept injections and attend monitoring visits according to the study schedule.

The study is expected to continue until December 2028.

Throughout your participation, all safety measurements and assessments will be repeated at regular intervals to track your health status and any changes over time.