Background: Detection of arterial oxygen saturation in pediatric patients with congenital heart disease (CHD) can be helpful for their management. Methods: We compared oxygen saturation and heart rate detected by pulse oximeter with the data of cardiac catheterization in order to determine the reliability and pitfalls of pulse oximetry (PO) in pediatric patients with CHD. 110 patients with different cyanotic and acyanotic CHD who were referred for right and left sided cardiac catheterization were enrolled in this study PO from left index finger and simultaneous oxygen saturations and pressures from cardiac catheterization were recorded. Results: There was a statistically significant correlation (r= 0.68, p