Switching of Sildenafil to Riociguat in CTEPH Patients

This study is testing whether switching from sildenafil (a common pulmonary hypertension medication) to riociguat can improve outcomes in patients with chronic thromboembolic pulmonary hypertension (CTEPH) — a type of high blood pressure in the lungs caused by old blood clots — who remain symptomatic after balloon pulmonary angioplasty (a procedure to open blocked lung arteries). **You may be eligible if...** - You have confirmed CTEPH with ongoing symptoms after balloon pulmonary angioplasty - You are currently taking sildenafil at a stable maximum tolerated dose for at least 6 weeks - You are in WHO functional class III (moderate-severe symptoms limiting activity) - You have not been hospitalized for pulmonary hypertension or heart failure in the past 30 days **You may NOT be eligible if...** - You have previously taken riociguat or similar drugs (soluble guanylate cyclase stimulators) - You are taking nitrates (e.g., nitroglycerin) or nitric oxide donors - You are pregnant or breastfeeding, or not using effective contraception - You have severely reduced kidney function - You have severe liver impairment (Child-Pugh C) Talk to your doctor to see if this trial is right for you.