Abstract: AIM:To evaluate the effect of ventilation with 0.5 L/L FiO2 in air or 1 L/L O2 following intubation on gas exchange. METHODS: One hundred and two patients (aged 1 month to 13 years) undergoing surgical cardiac intervention with congenital heart disease (CHD) (non-cyanosis) were given 1 L/L O2 for preoxygenation (3 min) and ventilation by mask (2 min). Following intubation, patients were randomly divided into two groups (51 patients in each group) and ventilated with either 0.5 L/L FiO2 in air or 1 L/L O2. Arterial blood gases were obtained for analysis before preoxygenation, 30 min following intubation, on entering the ICU, 30 min after extubation and 3 days postoperation. Subsequently, PaO2/FiO2 ratios were calculated. RESULTS: PaO2 values on entering ICU and 30 min after extubation were significantly improved in the group receiving 0.5 L/L FiO2 group than those in the group receiving 1 L/L O2. PaO2/FiO2 ratio in the 0.5 L/L FiO2 group was significantly improved at the following time points: 30 min after intubation, upon entering the ICU and 30 min after extubation. Mechanical ventilation time, time in ICU and length of hospitalization in 0.5 L/L FiO2 group were significantly shortened compared with those in the group receiving 1 L/L O2. CONCLUSION: During general anesthesia in children with CHD (non-cyanosis), ventilation of lungs with 0.5 L/L FiO2 is superior for improving gas exchange than ventilation of lungs with 1 L/L O2.