Switching of Sildenafil to Riociguat in CTEPH Patients

Inclusion Criteria: 1. Patients with established diagnosis of CTEPH who are symptomatic after Balloon pulmonary angioplasty (BPA) 2. Patients who are on stable maximally tolerated dose of sildenafil for at least 6 weeks as monotherapy, or in combination with other pulmonary hypertension specific therapies 3. WHO functional class III at screening 4. Stable dose of diuretics (if used) for at least 30 days at screening 5. No recent hospitalisation due to pulmonary hypertension or heart failure for at least 30 days Exclusion Criteria: 1. Previous treatment with riociguat other sGCs, or documented severe drug reaction or intolerance to sGCs 2. Use of nitrates or nitric oxide donors (eg, nitroglycerin, amyl nitrite, isosorbide dinitrate etc) by any administration routes within 30 days of screening 3. Pregnant women or breast-feeding women, or women with childbearing potential not using of combination of two effective contraception methods throughout study 4. Renal impairment with glomerular filtration rate \<15mL /min 5. Child-Pugh C hepatic impairment