A postal worker in St. Louis called Stray Rescue after finding the dog collapsed on the ground.
Rescuers said she wasn't moving when they got to her.
"Just the panic in the caller's voice, we knew that it was going to be a life or death situation and that minutes counted," Dr. Sarah Frei with Stray Rescue St. Louis told KTVI.
The veterinarian said her body temperature was so low a thermometer couldn't even read it.
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Even though the dog was in a coma, she is slowly making strides with constant care.
Officials are not sure how the dog got outside.
Pet owners are reminded to give their pets extra care during the colder months.