Peripheral pulse oximetry allows continuous non-invasive measurement of arterial oxygen saturation, but the gold standard for arterial oxygen saturation is co-oximeter which requires an arterial blood sample. The purpose of this research study is to determine the accuracy of a pulse oximeter with a standard sensor (Masimo LNCS sensor) versus with the study sensors, namely Masimo blue sensor and Nellcor Max-I sensors and compared against co-oximetry. Currently available peripheral oximeters (standard) are inaccurate at low oxygen saturation noted in children with cyanotic heart disease. Hence therapeutic interventions (including surgery and cardiac catheterizations) based solely on peripheral oximetry can be delayed and or inadequate. By doing this study the investigators will be able to establish correct limits of peripheral pulse oximeter when using the standard and the study sensors.