A snowboarder who was rescued after six days in the San Gabriel Mountains and given good chances for recovery died from a heart attack, a coroner said Saturday.

Jeff Thornton, 14, had developed difficulty breathing in the 24 hours before his death Friday, San Bernardino County Coroner's Deputy Linda Myers said.Thornton was being treated at Loma Linda University Medical Center for frostbite on his legs, arms and hands, dehydration, broken bones and an eye injury.

When he first entered the hospital, officials said Thornton was expected to remain for about a week and hadn't suffered any permanent injuries. But after suffering cardiac arrest, he could not be revived, Myers said.