Effect of Cold on the Isolated and Intact Rabbit Heart

¹ From the Department of Physiology, Arctic Aeromedical Laboratory, Seattle, Washington

The effect of cold on the isolated and intact rabbit heart was studied and compared with results previously obtained on the intact hypothermic dog. Neither the isolated heart nor the intact rabbit exhibited any cardiac arrhythmias as temperature was progressively reduced. In all instances gradual bradycardia occurred and eventually electrical and mechanical asystole developed at temperatures below 20°C. Ventricular fibrillation was produced in the isolated rabbit heart at normal temperature by electrical stimulation or the omission of glucose from the perfusion medium. The fibrillary state, however, consistently reverted to a normal pattern when the heart temperature was lowered to 27–24°C. The hypothermic dog, on the other hand, showed a high incidence of cardiac arrhythmias. The results indicate that a true species difference accounts for the cardiac response of the two groups to cold.