The ECC Guidelines 2000 considered interesting new evidence about a pre-defibrillation period of prescribed CPR to increase the probability that the postshock rhythm would be perfusing rather than asystole. If victims of out-of-hospital cardiac arrest have not received bystander CPR before the arrival of the defibrillator, a period of preshock CPR could enhance the value of the shocks. At the end of the year 2000 there was insufficient evidence to recommend any other approach than shock as soon as possible and perform CPR at all other times.