Objective To study the effect of Sildenafil in the treatment of hypoxemia after operation of cyanotic congenital heart disease.Methods A total of 34 cases with hypoxemia after operation of cyanotic congenital heart disease were collected between January 2009 to January 2015.They took Sildenafil with the dosage of 0.3-0.5 mg/kg every 6 hour.The change of heart rate (HR),systolic blood pressure (SBP),central venous pressure (CVP),pulmonary artery pressure (PAP),arterial partial pressure of oxygen [pa (O2)],arterial partial pressure of carbon dioxide [Pa (CO2)],oxygenation index [pa (O2)/FiO2],peak airway pressure (Ppeak),positive inotropic drug score (PIDS) and the lower bound of liver were observed at 4 time points,including before taking the medicine,after taking the medicine for 1 hour,after taking the medicine 1 day and after the ventilator was removed.Based on the data,the therapeutic effects of Sildenafil were studied.Results All 34 cases were cured.At the time point of 1 hour after taking Sildenafil,PAP,CVP and Ppeak decreased significantly,but pa (O2) and pa (O2)/FiO2 increased significantly (P ＜ 0.05).At the time point of 1 day after taking Sildinafil,SBP increased steadily,but PAP and CVP continued to get lower,and PIDS decreased significantly,while the liver lower bound was significantly reduced (P ＜ 0.05).At the time point of removing the ventilator,pa (O2) reached to (144.12 ± 26.25) mmHg,and hypoxemia was corrected,but PAP was reduced to (37.47 ± 3.77) mmHg,PIDS decreased to (17.56-± 1.94) scores,and heart failure was corrected.Compared with the previous 3 time points,there were statistically significant differences (P ＜ 0.05).Conclusion Sildenafil can highly selectively decrease pulmonary vascular resistance and obviously promote the correction of hypoxemia after operation of cyanotic congenital heart disease.