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How slow are a true hibernator’s breathing and heartbeat?

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The image shows a group of Virginia big-eared bats sleeping upside down in a dark cavern. — Dormancy Virginia big-eared bats (*Corynorhinus townsendii virginianushibernating*) are true hibernators, entering a state close to death for much of the winter.

True hibernators undergo a profound reduction in metabolic activity to survive adverse conditions, entering a state where their vital signs reach remarkably low levels.1

Heartbeat: The heart rate becomes so slow and gradual that it is often barely perceptible. For example, in the California ground squirrel, the heart may beat as slowly as once per minute at 5 °C (41 °F). In other deeply hibernating squirrels, the heart may beat only three or four times per minute.12
Breathing: Respiration is reduced to only a few breaths per minute.1

These physiological changes allow the animal to appear almost dead while maintaining enough internal regulation to survive. Unlike animals that merely sleep through the winter, true hibernators significantly lower their body temperature—often to near 0 °C (32 °F)—and require an hour or more of gradual warming to return to an alert state.1