Near infrared spectroscopy (NIRS) is a noninvasive tool used for continuous monitoring of regional tissue oxyhemoglobin saturation. Sensors are placed on the head and abdomen or flank and use light to measure the percent oxygen levels in tissues. Head NIRS has been correlated with oxygen levels of the blood returning from the brain, and an abrupt decline in post-operative cardiac patients has been shown in retrospective studies to predict an impending event such as cardiac arrest. Animal studies have demonstrated that somatic NIRS monitoring is able to detect flow-induced changes in regional oxygen levels of the kidney and gut directly under the sensor. Unlike cerebral NIRS monitoring, there is no data regarding the clinical utility of NIRS over the abdomen and flank in predicting outcomes. Children are at risk of decreased organ perfusion following cardiac surgery, and is a phenomenon termed low cardiac output syndrome (LCOS). It occurs in approximately 25% of neonates and young children following cardiac surgery. The effects of LCOS on end organ function, specifically the kidney may result in acute kidney injury, thereby increasing morbidity and mortality. The incidence of acute kidney injury (AKI) following cardiac surgery is reported as high as 40%. The use of NIRS in the operating room to detect AKI in pediatric patients undergoing cardiac surgery is the focus of this proposal Specific Aim 1: Determine if a reduction in renal NIRS intra-operatively identifies patients with AKI Hypothesis: Reduced intra-operative renal NIRS will precede the diagnosis of acute kidney injury by an increase in serum creatinine within 1 to 3 days post-cardiopulmonary bypass Specific Aim 2: Determine if a reduction in renal NIRS intra-operatively correlates with increases in emerging biomarkers of AKI.