An autopsy on Melbourne Cup favourite Admire Rakti has revealed the Japanese stayer died of heart failure.

"(The horse's death) is caused by a large heart mass, a really rapid heart rate that set up an irregular rhythm that didn't deliver enough blood to the body," Racing Victoria vet Dr Brian Stewart said.

Dr Stewart said vets working for trainer Tomoyuko Umeda had been flown in from Japan to assess Admire Rakti's condition before his Caulfield Cup win.

It was a routine that was repeated in the lead-up to the Melbourne Cup and on the day of the race when they declared the horse fit to run.

"Inevitably there will be instances like this," Dr Stewart said.

"In general, racehorses are very well looked after and very much loved by people.

"It happens in humans too so do we stop people running in marathons and people playing golf because someone might have a heart attack on the golf course."

Dr Stewart said a defibrillator could have saved Admire Rakti.

"We don't have equine defibrillators because the condition is so rare and the horse is such a large animal," he said.

"That would have been the treatment of choice if it had been done very quickly, but defibrillators, we will review. Whether it is practical, I don't know."

Dr Stewart said there were five vets on duty on Melbourne Cup day and the return-to-scale incident involving Araldo required two of his team to attend to the Mike Moroney-trained horse.

"In my role I would have normally been with (Admire Rakti) as it went back (to the raceday stalls), but there was an incident with Araldo," Dr Stewart said.

"We had a horse with a broken leg and I went to assist the other vet with Araldo in stabilising its injury.

"We didn't imagine there would be a fatal incident, they're so rare. A horse with a broken leg took my priority."

A full post-mortem report on Admire Rakti will take 10 days to complete.