Objective To compare dexmedetomidine with midazolam/fentanyl for sedation in children with pulmonary artery hypertension(PAH) after congenital cardiac surgery.Methods Forty children with PAH were randomly divided into two groups after congenital cardiac surgery.The age of children ranged from 3 to 89 months,and weight ranged from 3 to 26 kg.Group A received an infusion of dexmedetomidine(Dex) 0.5 - 1.0 μg/kg bolus for induction,then a maintenance dose of Dex 0.25 - 0.75 μg · kg- 1 · h - 1.Group B received an infusion of midazolam 0.1 mg/kg bolus for induction,then a maintenance dose of 0.5-2.0 μg·kg-1 ·min-1.The maintenance dose offentanyl was 1.0-1.5 μg·kg-1 · h-1.The time of target sedation score,duration of mechanical ventilation,frequency of using other sedatives and prevalence of delirium were compared between the two groups. Other indicators including COMFORT scale,heart rate ( HR),mean arterial pressure (MAP) and pulse oxygen saturation ( SPO2 ) were compared between the two groups among following time points:before infusion,10 min,1 h,4 h,8 h,12 h after infusion.Results Time points after infusion had lower COMFORT scale significantly compared with time points before infusion(26.3 ± 7.3 ) in group A ( P ＜0.01 ),so as in group B while the COMFORT scale was 23.9 ± 5.9 before infusion.There was no statistics difference of the time to reach the target sedation score between group A and group B [ (4.4 ± 1.5 ) min vs (4.3 ± 1.9 ) min,P ＞ 0.05].The COMFORT scale had no statistic difference among the time points after infusion in the two groups.The COMFORT scale,HR,MAP and SPO2 had no statistic difference between goup A and goup B among time points before and after infusion.Frequency of using other sedatives were significantly lower in group A compare with group B (4.3 ± 3.3 vs 10.7 ± 5.5 ) ( P ＜ 0.01 ).The prevalence of delirium was significantly lower in group A than group B (25％ vs 60％ ) ( P ＜ 0.05).The duration of mechanical ventilation was lower in group A compare with group B [ (40.9 ± 22.3) h vs (46.1 ± 23.1 ) h] but there was no statistics difference.Conclusion Compare with midazolam/fentanyl,single use of dexmedetomidine had sound therapeutic effects to provide sedation for children with PAH,while the latter could decrease the frequency of using other sedatives and prevalence of delirium.