There is also laboratory data that cooling during CPR may increase the rate of successful defibrillation. Boddicker et al. examined the success rates of defibrillation in swine cooled to different temperatures. After 8 minutes of VF (with no CPR), the animals were defibrillated with successive shocks as needed and underwent CPR until resumption of spontaneous circulation or no response. First-shock defibrillation success was highest in the hypothermia (33°C) group (6/8 hypothermia versus 1/8 normothermia; P=0.04). None of the 8 animals in the normothermia group achieved resumption of spontaneous circulation compared with 7/8 moderate hypothermia (P=0.001). Coronary perfusion pressure during CPR was not different between the groups, thus this beneficial effect of hypothermia was not due to alteration of coronary perfusion pressure but likely due to changes in the electrophysiological properties of the myocardium. Thus, it appears that mild hypothermia may have a beneficial anti-arrhythmic effect, as well as a neuroprotective effect.