Specific Aim 1: We will prospectively study 10 neonates (< 30 days of age) undergoing cardiac surgery utilizing cardiopulmonary bypass for arterial switch operation or Norwood operation to determine the specificity and sensitivity of a blood test for brain injury. This aim will be accomplished by analyzing blood samples for S-100 and NSE drawn prior to surgery, once each day following cardiac surgery as long as the patient remains in the intensive care unit (maximum 5 days)and at the time of postoperative brain magnetic resonance imaging. The S-100B and NSE values will then be correlated with brain magnetic resonance imaging studies before cardiac surgery and at following cardiac surgery.