We undertook a study to determine the ability of intravenous bretylium to cause "chemical defibrillation" or facilitate electrical defibrillation of hypothermia-induced ventricular fibrillation in the dog. Two groups of ten dogs were cooled to 22 C and placed into ventricular fibrillation. Following initiation of cardiopulmonary resuscitation, bretylium 15 mg/kg or normal saline was administered and the dogs were defibrillated according to a standard protocol. Both groups were equivalent in mean arterial pressure and arterial blood gases throughout the investigation. Seven dogs in each group were converted from ventricular fibrillation to an organized cardiac rhythm (P greater than .05). Despite the possible value of prophylactic bretylium in the setting of hypothermia, its use as active treatment for hypothermia-induced ventricular fibrillation in dogs does not seem to be beneficial.