Garrett Blois fell on a sidewalk on Greenfields Drive at about 7:55 a.m.
He was rushed to the Dr. Everett Chalmers Hospital, where he was pronounced dead.
The Fredericton Police Force has been investigating the boy's sudden death.
An autopsy was conducted in Saint John on Tuesday morning and the results were released at 3:30 p.m.
It's unclear whether there is any family history of heart problems, said Insp. Gary Forward, who heads the force's major crime unit.
"I think that's one of the things that we're still looking into as part of the investigation," he said.
"Obviously there's more information that we have to glean from the pathologist and that’s certainly ongoing."
Garrett did not have any known health conditions, his grief-stricken father had told CBC News on Monday night.
Police have not yet received the final toxicology report, Forward said.
But investigators have "no indication to believe that this is criminal in any nature," he said, with evidence suggesting "that this was in fact a health-related issue."
Police have also ruled out the possibility that it was a "slip and fall accident," according to Forward.
"Out of courtesy for the family, no more information will be released at this time," he said.Suggest a correction