Objective Endothelin is a key role in the pathogenic of pulmonary arterial hypertension. High concentrations of endothelin-1 have been recorded in plasma and lungs of patients with pulmonary artery hypertension associated with congenital heart disease, and the concentrations of endothelin-1 was correlated with severity degree of pulmonary arterial disease.Endothelin exerting vasoconstrictor and mitogenic effects by binding to two distinct receptor isoforms in the pulmonary vascular smooth muscle cells: endothelin A and B receptors. Bosentan is an orally active dual ( A and B) endothelin receptor antagonist that has been shown to improve exercise capacity, haemodynamics, and clinical worsening in many clinical trials, but have no experience in post-operation of congenital heart disease with PAH. In our country, there are lots of elder patients of congenital heart disease accompany with pulmonary arterial hypertension. And they have poor prognosis after operation because pulmonary arterial hypertension leads to right ventricular failure and sudden death. So we hope bosentan can improve clinical outcome of these patients. This time we present the results of the bosentan trial in post-operative patients still with pulmonary arterial hypertension, a randomized controlled trial designed to assess the efficacy and safety of the dual endothelin receptor antagonist bosentan in post-operative pulmonary arterial hypertension, and present the first experience of bosentan for these patients.Methods This study was a prospective clinical trial. The objects were 30 patients ( age:4 months - 6.8years,weight:5 - 15 kg) who still had pulmonary artery hypertension at one week after cardiac defects repaired. They were randomized to controlled ( n = 15 ) or to bosentan ( n = 15 ). Dosage regimen: 10 - 20 kg patients, 31. 25 mg qd ( 4 weeks ) ,31.25 mg bid ( 8 weeks);5 - 10 kg patients, 15.6 mg qd ( 4 weeks), 15.6 mg bid ( 8 weeks). Evaluate the efficacy and safety of Bosentan through the amelioration of pulmonary arterial systolic pressure, WHO functional class, and clinical worsening. Results We monitored pulmonary arterial systolic pressure after operation by echocardiogram 2 times, baseline ( 1 week after operation) and at 12 weeks later. The pulmonary arterial systolic pressure decreased 19.5 mm Hg in Bosentan group( P =0. 000), and decreased 10.3 mm Hg in control group(P =0. 164), with the mean treatment effect of 9.2 mm Hg (P=0.049,95%CI:0. 1 -18.3). The effct of bosentan on haemodynamics is also reflected in the reduction plasma ET-1 concentration in bosentan group. Plasma ET-1 in control group increased (0. 15 ±0.1 )fmol/ml(P =0.77), however, decreased (2.01 ±0.3)fmol/ml (P=0. 03) in bosentan group; Bosentan prevented post-operation PAH. Bosentan treatment was associated with lower incidence of worsening NYHA functional class compared with controlled(0 in the bosentan group vs 13% in the placebo group) There was a delay in time to clinical worsening with bosentan compared wih controlled group. Abnormal liver function occurred in 2 cases in bosentan group but resolved after discontinuation of bosentan treatment, no other side effects. Bosentan produced hemodynamic improvement and was well tolerated in infant. Conclusion Bosentan administration in patients with postoperative PAH is safe and efficient. Bosentan is a new effective approach to therapy for postoperative pulmonary arterial hypertension in children.