An international team of researchers looked at 49,555 out-of-hospital cardiac arrests that occurred in major U.S. and Canada cities. They analyzed a key subgroup of these arrests, those that occurred in public, were witnessed and were shockable. The researchers found that nearly 66 percent of these victims survived to hospital discharge after a shock delivered by a bystander. Their findings emphasized that bystanders make a critical difference is assisting cardiac arrest victims before emergency responders can get to the scene.