Age 18–75 years, WHO Group 1 PAH confirmed by right heart catheterization (mPAP ≥25 mmHg, PCWP ≤15 mmHg), Stable oral monotherapy (PDE5 inhibitor, ERA, or riociguat) for ≥30 days, Baseline 6MWD ≥ 150 m. Here, PDE5A is linked to pulmonary arterial hypertension.