The finding of second-degree and high-grade atrioventricular block in a patient with severe accidental hypothermia is described. Additional findings included atrial fibrillation, severe sinus bradycardia, and prominent J (Osborn) waves. This case represents, to the authors' knowledge, the first report of advanced spontaneous AV block not induced by atrial pacing in severe accidental hypothermia. Reversal of the block, and other characteristic changes, suggest a relationship to low temperature.