Bosentan Therapy in Children With Functional Single Ventricle

Inclusion Criteria: * Signed informed consent obtained from patient's legally acceptable representative. * Pediatric patients waiting for staged Fontan procedure with high risk of increased PVR after bidirectional cavopulmonary connection (BCPC) * Transpulmonary pressure gradiant (TPG) \> 10mmHg when the obstruction of anastomosis and lung problem were excluded. * With the diagnosis of high risk of increased PVR, such as associated with TAPVC, after pulmonary artery banding, after systemic to pulmonary shunt more than 6 months, and et al. * Diagnosed as increased PVR with catheterization. Exclusion Criteria: * PAH associated with conditions other than those mentioned above, e.g., iPAH, PAH secondary to portal hypertension, HIV patient with opportunistic infection * Psychotic, addictive or other disorder limiting the ability to provide informed consent or to comply with study requirements * AST and/or ALT \> 3 times the upper limit of normal ranges. * Hemoglobin concentration \< 75% the lower limit of normal ranges * Treatment or planned treatment with another investigational drug within 3 months of screening * Treatment with calcineurin-inhibitors (e.g., cyclosporine A and tacrolimus), fluconazole, glibenclamide (glyburide) within 1 week of enrollment of this study * Known hypersensitivity to bosentan or any of the excipients