To measure survival to hospital discharge of patients with out-of-hospital cardiac arrest in community units (e.g., apartment or office buildings, gated communities, sports venues, senior centers, shopping malls) served by trained non-medical responders using automated external defibrillators (AEDs), an approach called Public Access Defibrillation, compared to units receiving the traditional optimum community standard of care (i.e., rescuers trained to recognize a cardiac emergency, call 911, and initiate CPR).