This study will involve the use of therapeutic hypothermia. This prospective cohort pilot study will evaluate the clinical performance of a new device, the ThermoSuit™ System, to achieve therapeutic hypothermia in comatose patients following resuscitation from cardiac arrest, and the impact of the vasodilator, magnesium sulfate, on cooling performance and hemodynamics in these patients. The study hypothesis is that magnesium sulfate will significantly increase the rate of cooling.