Hyperthermia is an abnormally high body temperature caused when a body produces or absorbs more heat than it dissipates.
Authorities say 2-year-old William Jensen and his 4-year-old brother, Tyler, became fatally overheated six weeks ago.
Their mom had left them inside her Toyota 4Runner with the heater running, as she spoke to a male friend for 90 minutes. The coroner's report says the deaths were accidental.
WATCH: How hot does a car heater get in two hours?
The mother, Heather Jensen, told investigators that she took her sons to play in the snow near the Powderhorn Ski Resort on November 27. Then, she allegedly put them into the car while she spent time talking with her friend in his car.
After Heather Jensen returned to her Toyota 4 Runner to drive off, she noticed one of the boys was not breathing.
Paramedics could not revive 2-year-old William. The older son, Tyler, was airlifted to Children's Hospital, but he died several days later. First responders initially thought the kids may have suffered carbon monoxide poisoning, however the coroner's investigation found otherwise.
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It is rare for children to die of hyperthermia in hot cars in cold weather months; however, 9Wants To Know discovered a handful of similar cases across the country in the last decade.
The Mesa County District Attorney is reviewing investigative reports to determine whether Heather Jensen should be criminally charged in her children's deaths.
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