Vardenafil Inhaled for Pulmonary Arterial Hypertension PRN Phase 2B Study is exploring a new medicine, RT234, to help people with Pulmonary Arterial Hypertension (PAH). PAH is a condition that makes it hard for your heart and lungs to work together, causing trouble when exercising. This study will check if a single inhaled dose of RT234 can help improve exercise ability and reduce breathing difficulties. To join, you need to be between 18 and 80 years old, diagnosed with PAH, and able to walk and exercise independently. The study will involve several visits and tests, such as walking and breathing tests (CPET and 6MWT), to see how well RT234 works compared to your usual health measurements. You must also be willing to follow all study rules and procedures.

• The study involves multiple visits and tests over time.
• Participants must be willing to follow all study rules.
• There are specific health conditions and medications that may prevent participation.