Novel non-invasive optical instrumentation including near infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS) increase our ability to measure cerebral hemodynamics and oxygenation in real time. NIRS measurement of cerebral oxygenation has been rapidly accepted into clinical practice, but has not been rigorously studied. DCS for measuring cerebral blood flow, is a more recent innovation in optical imaging. Used in combination DCS and NIRS expand our capability to study how cerebral hemodynamics and cerebral metabolism are affected by clinical care following early heart surgery. Further, using DCS to continuously assess cerebral blood flow we will be able to assess cerebral autoregulation by performing new time-series correlation analysis with mean arterial blood pressure. Cerebral autoregulation is a protective mechanism loosely defined as the ability to maintain constant and adequate cerebral blood flow despite fluctuations in systemic blood pressures, may become dysfunctional as a consequence of critical illness. Using these new optical instruments we plan to study the timing and causes of brain injury in the form of periventricular leukomalacia (PVL) in infants with severe forms congenital heart defects (CHD) that require infant heart surgery. In infants with CHD the PVL injury occurs in 20% before surgery and just over 50% afterwards. By monitoring brain tissue blood oxygenation, flow, and metabolism after infant heart surgery, we will investigate the cerebral hemodynamic risk-factors for developing new or worsened PVL injury in CHD patients. A better understanding of the timing and causes of PVL in this population will help physicians build strategies to treat or prevent it. Furthermore, the knowledge gained from this study will help design studies for other 'at- risk' populations of infants, such as premature infants or infants who have had birth trauma.