In the preoperative management of congenital heart disease (CHD) with increased pulmonary blood flow, hypoxic gas management to control pulmonary blood flow is useful. However, the cerebral oxygenation state has rarely been studied, and there is concern about neurologic development. In eight infants with CHD accompanied by increased pulmonary blood flow, hypoxia was induced after a 1-h baseline period in room air (FiO2, 0.21). The infants were simultaneously monitored in both the front-temporal region and the right-brachial region for 90 min using near-infrared spectroscopy (NIRS). The minimum SaO2 (pulse oximetry) after hypoxic gas administration was 80.8 +/- 2.9% when the minimum FiO2 was 16.2 +/- 1.1%. With a decrease in SaO2, oxy-Hb (O2Hb) decreased and total Hb [cHb: O2Hb + deoxy-Hb (HHb)] increased in both regions in the majority of infants. HHb increased in both regions with a decrease in SaO2. The maximum change in the tissue oxygenation index (TOI: O2Hb/cHb x 100) was -8.3 +/- 2.6% in the front-temporal region and -3.6 +/- 2.3% in the right-brachial region. Cerebral oxygenation decreased despite an increase in cerebral blood flow during hypoxic gas management. The change in TOI was < or =10% when the SaO2 was > or =80%. Safer control of SaO2 should be maintained over 80% for hypoxia management in CHD based on the results of the present study.