'Deadliest Catch' Star Tony Lara -- Died From a Heart Attack in His Sleep

"Deadliest Catch" star Tony Lara didn't suffer when he died ... authorities believe he suffered a heart attack in his sleep.

Meade County Sheriff, Ron Merwin, tells TMZ ... the pathologist who performed the autopsy observed scar tissue on Lara's heart, which is consistent with the effects of a heart attack.

Merwin says they'll know for sure when the toxicology report comes back, but there were no signs drugs or alcohol played a role. We're told Lara's body is being transferred back to his hometown in Alaska.