Cardiac arrest is a common and catastrophic event with substantial human and financial costs. It is well understood that cardiac arrest leads to brain injury. However, what is not widely appreciated is that, after circulation has been restored, cerebral hypoperfusion continues. Ongoing cerebral vasoconstriction and cerebral hypoxia has been demonstrated using technologies that include positron emission tomography, ultrasound, jugular bulb oxygen saturation and cerebral oximetry.