A final necropsy report on Yukon musher Yuka Honda's sled dog Firefly has determined that the animal died of heart failure, during last month's Yukon Quest.
The report also ruled out the booties Firefly had eaten as a cause of death.
Firefly died on the Quest trail, shortly before reaching the race's halfway point in Dawson City.
A preliminary necropsy report said the dog had eaten several booties and had an enlarged heart.
The race's head veterinarian, Cristina Hansen, says it's relatively common for sled dogs to have enlarged hearts, and experience heart murmurs. Firefly's heart condition was detected by vets before the race, but Hansen said it wasn't deemed significant.
"That's not something that necessarily sets of alarm bells," she said.
On the trail, Hansen said the electricity in Firefly's heart simply stopped "conducting normally". She says the musher would have had no warning that something was amiss.
"That's the same with human athletes that have heart conditions and that have sudden deaths during their sport. They're running and active and doing their sport and then they fall over dead."
Hansen also said there was no evidence that the dog's "stomach full of booties" was a factor in the death.
Firefly was the only dog to die during this year's Yukon Quest. Honda opted to drop out of the race rather than continue beyond Dawson City.
Another of Honda's dogs died during the 2007 Yukon Quest. Race officials that year determined that Jewel choked to death after Honda's 14-dog team got away on her.