The heart rate declines slowly during the next few hours in Rana sylvatica until arrest occurs nearly 24 h after the onset of freezing (Layne et al. 1989). Interestingly, freeze-tolerant and freeze intolerant frog species differ very little in this overall sequence (Lotshaw 1977, Costanzo et al. 1993b), whichfurther attests to the fact that freezing is not instantaneously lethal to most frog species