Objective To investigate the effects of eardiopulmonary bypass(CPB)on plasma nitric oxide (NO)and asymmetric dimethyl arginine(ADMA)concentrations in patients with congenital heart disease complicated with pulmonary hypertension undergoing open heart surgery.Methods Eighteen ASA Ⅱ or Ⅲ patients aged 11-40 yr weighing 26-59 kg undergoing open heart surgery under CPB were divided into 3 groups according to pulmonary arterial systolic pressure(PASP)(n=6 each):group Ⅰ PASP<30 mm Hg;group Ⅱ PASP 30-50 mm Hg and group Ⅲ PASP>50 mm Hg.Arterial blood samples were taken before induction of anesthesia (To,baseline),at the start and termination of CPB(T1,2)and 3,6,24 h after CPB(T3-5)for determination of plasma NO and ADMA concentrations.Results The three groups were comparable with respect to M/F sex ratio,age,body weight and CPB time.The plasma ADMA concentrations were significantly increased while NO concentrations were significantly decreased at termination of CPB(T2)and 3 and 6 h after CPB(T3,4)as compared with the baseline at T0 in group Ⅱ and Ⅲ.The plasma ADMA concentration were significantly higher and No concentrations were significantly lower at all time points in groupⅡand Ⅲthan in group Ⅰ.Conclusion CPB can increase plasma ADMA concentration and decrease plasma NO concentration in patients with congenital heart disease complicated with pulmonary hypertension undergoing open heart surgery.