alt Hacker NewsI believe this is common to attempt when dealing with very cold water drownings. Obviously this is a very extreme case, but I believe you'd generally be instructed on the phone to start CPR but not try to heat them up until the ambulance arrives. Just in case.
The case below had a person conscious in the water for 40 minutes (with an air pocket under the ice) before going into circulatory arrest, and then spent another 40 minutes clinically dead in under water. The combined 80 minutes in the water lowered her body temperature very dramatically, and played a large part in her almost complete recovery.