Medina Spirit collapsed near the finish line just as he was completing a workout and died immediately, the CHRB told CNN.
"Following the completion of a routine morning workout, Medina Spirit collapsed on the track at Santa Anita Park and died suddenly of a probable cardiac event according to the on site veterinary team who attended to him," Santa Anita Park said in a statement.
The news was also confirmed by its Hall of Fame trainer Bob Baffert, who said the 3-year-old champion colt died from a "heart attack" following a workout, but the racing board will not determine cause of death until a necropsy and toxicology tests are complete. The examination and tests will be conducted at the University of California, Davis.
"My entire barn is devastated by this news," Baffert's statement read.
"Medina Spirit was a great champion, a member of our family who was loved by all, and we are deeply mourning his loss. I will always cherish the proud and personal memories of Medina Spirit and his tremendous spirit."
As well as being an exciting racehorse, Medina Spirit was the subject of one of the sport's biggest controversies in the United States earlier this year.
After crossing the line first in this year's Kentucky Derby, the horse failed a post-race drug test.
Trainer Baffert was subsequently banned from fielding any horses at the Churchill Downs racetrack for two years following the confirmation of the test for a legal drug whose presence is banned on race day.
Baffert later provided a lengthy statement claiming an ointment used to treat dermatitis may have caused the positive test.
The Kentucky Horse Racing Commission said the investigation into the test is ongoing and paid tribute to the thoroughbred.
"The Kentucky Horse Racing Commission (KHRC) is saddened to hear of the death of Medina Spirit. He was a valued member of the thoroughbred industry's horse racing family."
Medina Spirit raced four more times after the Derby, finishing third at the Preakness Stakes and winning two races in California. And he was second in the prestigious Breeders' Cup Classic in early November.
He won half of his career 10 starts.
A statement from the Santa Anita racetrack confirmed a full necropsy will take place to determine the exact cause of the sudden death.
The racetrack has an unwanted record of equine fatalities, which prompted an investigation in 2019.
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