Finding the Optimal Cooling tempeRature After Out-of-HoSpiTal Cardiac Arrest

Inclusion Criteria: * Signed informed consent (obtained from their legal representative) * 18 years of age or older and less than 80 years old. * Witnessed OHCA of presumed cardiac cause * Sustained ROSC (when chest compressions have not been required for 20 consecutive minutes and signs of circulation persist) * Initial shockable cardiac rhythm (documented by ECG or AED) * Interval from collapse to advance life support \< 20 minutes * Interval from collapse to ROSC \< 60 minutes * Lack of meaningful response to verbal commands upon arrival to hospital after suffering non-traumatic cardiac arrest in an out-of-hospital setting * Systolic blood pressure of \>90 maintained for a least 30 minutes post-ROSC without pressors, or with a stable dose of pressors Exclusion Criteria: * Traumatic cardiac arrest * Toxicological etiology * Known or suspected pregnancy * Do Not Attempt to Resuscitate order in force * Unwitnessed arrest * In-Hospital arrest * Anatomy, previous surgery or disease state contraindicating femoral venous access * Received neuromuscular blocking agents prior to assessing level of consciousness following ROSC * Neurological evaluation insufficient/incomplete after ROSC but prior to randomization. * Body core temperature \< 34ºC at randomization * Current Inferior Vena Cava (IVC) filter * Known history of acute neurological illness or severe functional disabilities prior to arrest (e.g., seizures, traumatic brain injury, increased intracranial pressures, intra-cerebral hemorrhage, etc). * Known hypersensitivity to hypothermia including a history of Raynaud's disease * Suspected or confirmed acute intracranial bleeding * Suspected or confirmed acute stroke * Terminal illness or life expectancy of less than 3 months prior to arrest * Currently enrolled in another investigational new drug or device trial that has not completed the primary endpoint or that clinically interferes with this Trial's endpoints (For the purpose of this protocol, subjects involved in extended follow-up trials or registries for products that are currently commercially available are not considered enrolled in an investigational trial). * Transferred from a non-participating hospital.