Scientists have previously performed the procedure on pigs with a 90 percent success rate. In most cases, the animals' hearts began beating again on their own after their blood was replaced. Their physical and mental functioning was unharmed. In 2006, scientists in Boston induced hypothermia and a slowed heart rate in mice by using hydrogen sulphide gas. The mice returned to normal two hours after they began breathing normal air again.

"After we did those experiments, the definition of 'dead' changed," surgeon Peter Rhee at the University of Arizona in Tucson, who led the pig experiment, told the New Scientist. "Every day at work I declare people dead. They have no signs of life, no heartbeat, no brain activity. I sign a piece of paper knowing in my heart that they are not actually dead. I could, right then and there, suspend them. But I have to put them in a body bag. It's frustrating to know there's a solution."

The new procedure, called "emergency preservation and resuscitation," will be attempted on humans only in extreme cases. The patients will have entered the ER with severe blood loss and will have, on average, less than a 7 percent chance of surviving otherwise.

Though these will be the first such human clinical trials, several freak accidents have previously revealed how extreme cold can preserve human life. In 1999, Swedish radiologist Anna Bagenholm survived 80 minutes under a layer of ice in freezing water after a skiing accident. Her body temperature plunged to 56.7 degrees Fahrenheit. In 2000, a toddler from Edmonton, Alberta, wandered into the freezing winter wearing nothing but a diaper, and she survived two hours without a heartbeat before coming back to life.

Then there was Janice Goodger, a 64-year-old woman in Duluth, Minnesota who was found frozen and without a pulse on her icy driveway one morning in 2008. She recovered fully in a hospital later.

"The next day, she was doing so well, they wanted to run tests on her," said Mark Roth of the Fred Hutchinson Cancer Research Center in Seattle. "She got cranky and just went home."