Bosentan Effects in Inoperable Forms of Chronic Thromboembolic Pulmonary Hypertension

Inclusion Criteria: * Symptomatic pulmonary hypertension in modified NYHA functional class II to IV due to CTEPH as demonstrated by ventilation/perfusion lung scanning and pulmonary angiography. * CTEPH judged inoperable because of peripheral localization of thrombotic material or persistent or recurrent pulmonary hypertension after pulmonary endarterectomy (PEA) with no evidence of recurrent thromboembolism and not amenable to repeated surgery. * 6-minute walk test (6MWT) distance \< 450 m. * Hemodynamic evaluation showing: Mean pulmonary arterial pressure (mPAP) \>= 25 mmHg; Pulmonary capillary wedge pressure (PCWP) \< 15 mmHg; Pulmonary vascular resistance (PVR) at rest \>= 300 dyn×sec/cm5 * For patients who underwent PEA, hemodynamic evaluation must have been performed more than 6 months after PEA. * For all patients, hemodynamic evaluation must have been performed with the 3 months immediately preceding inclusion. * Men or women \>= 18 and =\< 80 years of age (Women of childbearing potential must have a negative pre-treatment pregnancy test and use a reliable method of contraception). * Anticoagulants at efficacious dose for at least 3 months prior to randomization. * Signed informed consent prior to initiation of any study-mandated procedure. Exclusion Criteria: * Other forms of pulmonary hypertension including pulmonary hypertension related to sickle cell disease. * Obstructive lung disease: FEV1/FVC \< 0.5 after bronchodilator. * Severe restrictive lung disease: To…