We need to conduct a pilot study of hypothermia therapy following cardiac arrest at 11 Children's Hospitals to test the feasibility of recruitment and to test the appropriateness of our inclusion/exclusion criteria prior to proceeding to a large multi-centre trial. We chose 11 large children's hospitals with large cardiac arrest populations with a track record of resuscitation research to improve the feasibility of patient recruitment into this pilot study. The pilot data will be used to do a sample size calculation for the larger randomized controlled study. It will also be important to demonstrate enrolment in an important sub-group of patients, those being placed on ECMO post-arrest. Patients randomized to cooling on ECMO will have rapid core cooling via the extracorporeal circuit and this rapid cooling may lead to a more pronounced therapeutic effect.