With the increasing use of cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest (DHCA) to support cardiac surgery in the newborn period, it is critical to understand the acute and late effects of hypothermia and complete or partial ischemia on energetics and cell viability in the developing brain. Protection of the neonatal brain under these conditions has been effective but is still incomplete. 1 , 2 Improved support for children during and after DHCA will be critical in improving neurological outcome.