The TAME Cardiac Arrest trial will study the ability of higher arterial carbon dioxide (PaCO2) levels to reduce brain damage, comparing giving patients 'normal' to 'slightly higher than normal' blood PaCO2 levels and assessing their ability to return to normal life-tasks. It will be the largest trial ever conducted in heart attack patients in the intensive care unit. This therapy is cost free and, if shown to be effective, will improve thousands of lives, transform clinical practice, and yield major savings.