Out-of-hospital cardiac arrest, a condition characterized by a person suddenly collapsing due to heart stoppage, is a leading cause of death in the United States. In out-of-hospital cardiac arrest, survival is dependent upon what the American Heart Association has termed the chain of survival which includes quick activation of the 9-1-1 system, prompt cardiopulmonary resuscitation (CPR), early defibrillation, and qualified advanced life support care (paramedic care). CPR allows for some circulation and delivery of oxygen to vital organs when the heart is no longer beating on its own. However, in some instances, the citizen bystander has not been trained in CPR, presenting a circumstance where the cardiac arrest victim may not receive CPR until the arrival of emergency medical services (EMS) personnel (i.e., paramedics). The delay in CPR adversely affects outcome and dcreases the chance of survival. In response to this need, the EMS Division of Public Health - Seattle and King County developed and instituted telephone CPR instructions that could be provided "on-the-spot" during a cardiac arrest by the emergency medical (9-1-1) dispatcher. The instructions are designed to be given over the phone to persons who have not had previous CPR training so that they can initiate CPR prior to the arrival of EMS personnel and have been termed "dispatcher-assisted" CPR. The dispatcher instructions provided by the dispatch agencies of King County include the standard "full" CPR protocol of ventilations (breathing into the victim's mouth to inflate the lungs) and chest compressions(pumping on the patients chest to help circulate the blood). The ventilations oxygenate the blood while the chest compressions pump the oxygenated blood forward. This EMS program has led to a considerable increase in the proportion of cardiac arrest victims in King County that receive citizen bystander CPR prior to EMS arrival and has been associated with improved survival (appendix 1).