The crucial links in the chain of survival include
Early access to emergency care: The earlier a bystander recognizes that cardiac arrest has occurred, the sooner someone can call emergency medical services, and the sooner personnel will arrive on site to deliver advanced care.
Early cardiopulmonary resuscitation (CPR): The sooner the rescuer starts CPR (particularly chest compressions), the greater the chance the brain and other vital organs will receive enough oxygen to keep the person alive until an automatic external defibrillator (AED) can be used or more advanced medical care provided.
Early defibrillation: Sometimes an electrical shock, called defibrillation, needs to be given to restore the heart's normal rhythm. The sooner this is done, the better.
Early provision of advanced medical care: The sooner emergency medical services (EMS) personnel can take over what the rescuer started, the sooner the person can benefit from advanced medical care.
People who are resuscitated need advanced monitoring and treatment and eventually rehabilitation and other measures to improve recovery.