Objective: to investigate the characteristic and the correlation of pH, PO2, SO2 , HCO3 between arterial and venous blood gas in children with congenital cyanotic heart disease, right to left intracardiac shunting. Study design: cross descriptive study. Result A total of 64 simultaneous venous and arterial blood samples were obtained from 64 patient addmited to the pediatric department in Hue Central Hospital with congenital cyanotic heart disease, right to left intracardiac shunting from 5/2010 to 6/2011. Mean values of pH, SO2, PO2 from arterial and venous blood samples are less than normal values. pH, PaO2, HCO3- and SaO2 from arterial blood sample in children with congenital cyanotic heart disease, right to left intracardiac shunting with decreasing pulmonary flow are less than ones with increasing pulmonary flow. pH, SvO2, PvO2 from venous blood sample in children with .congenital cyanotic heart disease, right to left Intracardiac shunting with decreasing pulmonary flow are less than ones with increasing pulmonary flow. pH, PO2, SO2 , HCO3- were all significant correlated in arterial blood gas and venous blood gas. There isn't difference between the pH venous blood and the pH arterial blood. Conclusion: There are a significant correlation in pH, PO2, SO2 , HCO3- among arterial blood gas and venous blood gas values. pH venous blood may be useful alternative to arterial sample for children with congenital cyanotic heart disease, right to left intracardiac shunting.