This study is looking at how a medicine called **treprostinil** can help people with a lung condition called **pulmonary arterial hypertension (PAH)**. PAH makes it hard for the heart to pump blood to the lungs. The study wants to see if treprostinil can lower the pressure in the lungs and improve heart function. Participants need to have confirmed PAH and meet specific health criteria. They should not have used certain medicines before and must be ready to take other PAH medicines if needed. The study will measure things like **mean pulmonary artery pressure (mPAP)**, which is the average pressure in the lung arteries, and how well the heart's right side is working.

**Key Points:**

• Participants will need to take treprostinil and possibly other PAH medications.
• There are specific health criteria for joining, including no recent use of certain drugs.
• Participants must be able to undergo certain tests and procedures during the study.