Abstract： Objective To investigate the effect of cold water immersion on the cardiac function of dogs. Methods Four healthy dogs were immersed in cold water at ( 6 ± 1 ) ℃ until the onset of ventricular fibrillation. Electrocardiogram was recorded with Cardiofax, cardiac function was monitored with the polygraph system, and changes in the structure of myocardium were observed with the transmission electron microscope.Results With the decrease in the body temperature of animals, marked changes in the decrease of the left ventricular pressure peak value (LVSP) and isovolumetric contraction of maximal ascending/descending velocity ( ± dp/dtmax) could be noted. When high -grade hypothermia occurred, J wave was found with a prolonged Q-T duration, and subsequently, there came the rapid ventricular arrhythmia. Conclusions Hypothermia could induce the decrease in the canine cardiac function, moreover, the prolongation of Q-T and the appearance of J wave might predict the occurrence of ventricular fibrillation.