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.

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 we will be able to establish correct limits of peripheral pulse oximeter when using the standard and the study sensors.

The investigator hopes to learn the limits of accuracy of currently available and used pulse oximeters. In children with cyanotic heart disease the "blue sensor" has been found in small studies to be more accurate compared to the "standard" pulse oximeter.

This study is important as it will provide information as to which pulse oximeter should be routinely used in children with cyanotic heart disease and to assess which SPO2 even with blue sensor is borderline and therefore the physician will know to obtain arterial blood sample for co-oximeter prior to planning important procedures based on a saturation reading.

Inclusion Criteria:

1. Children from LPCH undergoing cardiac catheterization or heart surgery in SUMC or LPCH respectively
2. Peripheral arterial saturation less than or equal to 90% at time of enrollment
3. weigh between 3-20 kg
4. Less than or equal to 10 years of age

Exclusion Criteria:

1. Lack of consent
2. Greater than 10 years of age
3. Less than 3 kg or more than 20 kg in weight
4. Peripheral arterial saturation greater than 90% at time of enrollment
5. Lack of arterial access

Children with cyanotic heart disease undergoing cardiac catheterization or heart surgery in Stanford University Medical Center(SUMC) or Lucile Packard Children's Hospital(LPCH) respectively with peripheral arterial saturation less than 90% at time of enrollment.