A recursive estimation model is used to investigate the roles of cardiopulmonary resuscitation (CPR) and advanced life support in improving survival from out-of-hospital cardiac arrest. The importance of life support measures is clearly evidenced in the analysis: Fewer elapsed minutes between the cardiac arrest and the start of CPR increase the probabilities of both a favorable cardiac rhythm and defibrillation and the probability of survival. Similarly, a shorter elapsed time between the start of CPR and defibrillation is significantly related to a higher probability of survival of the cardiac arrest. Personal characteristics also contribute to survival, but primarily via their association with a favorable initial postarrest cardiac rhythm and the probability of defibrillation. The initial postarrest cardiac rhythm is shown to be an indicator of the heart's condition, but when other factors associated with survival are included in the analysis, it does not independently influence an individual's probability of survival.