Participating research sites identified 1,000 units (e.g., public areas, gated communities, shopping malls, airport terminals, casinos, business parks) within their service area that anticipated at least 0.6 treatable out-of-hospital cardiac arrests within a 15 month period. Each unit was randomized to serve as either an intervention or control group, with comparative episode data collected for a 15 month period following a short preliminary data collection period (approximately 2 months to evaluate the ability for the site to capture event data) after training. Within each site, units were sub-randomized to a retraining strategy. Performance at retraining was monitored, and strategies modified if indicated.