Children with congenital heart disease (CHD) are prone to present abrupt changes in cardiovascular functions which cause hypoxic spells or acute heart failure, so that oxygen monitoring during dental treatment is of great importance in cyanotic CHD patients. Monitoring of arterial oxygen saturation (SpO2) by pulse oximetry has several advantages, including rapid response time, freedom from skin injury, self-calibration and continuous readout of the SpO2 value. In these studies, SpO2 was measured in 68 pediatric patients (55 were CHD children and 13 were normal children) during dental treatment at the Pediatric Dentistry, Hokkaido University Dental Hospital. In all of the normal patients, SpO2 did not desaturate less than 95%. On the other hand, SpO2 ranged from 56% to 98% in CHD patients, and in 22% (n = 12) of these, SpO2 desaturated below 80%. All of the SpO2 less than 80% patients had been diagnosed as cyanotic CHD. Classification of CHD cases (n = 144, the total number of measurements) on the pattern of the SpO2 variation revealed that in 11% (n = 16) of the CHD cases, SpO2 decreased during dental treatment. Twelve of these 16 cases could not readily accept dental treatment. We suggest that behavior management is the most important factor in CHD patients for keeping SpO2 stable. Motion artifact of the SpO2 value, which was easily evoked when a patient bent his elbow or shook his finger, often made the pulse oximetry useless. In our studies, the SpO2 value sometimes became inaccurate in fearful infants or handicapped patients. Pulse waveform displayed on the front panel of pulse oximetry was useful to identify the motion artifact. We conclude that pulse oximetry is an appropriate apparatus for continuous arterial oxygen monitoring in pediatric patients during dental treatment as far as motion artifact is effectively eliminated.