Racing Victoria's Head of Veterinary and Equine Welfare Brian Stewart said an autopsy was conducted on Tuesday night at the University of Melbourne and initial results pointed to acute heart failure.
Dr Stewart initially said the horse suffered from "sudden death syndrome'', which occurs in just 0.007 per cent of racehorses.
"It's usually one of two things, either through heart rhythm or ruptured blood vessels in that they bleed out internally," he said.
"We won't know which until the post mortem is done."
He said an irregular heartbeat which progressed to a condition called ventricular fibrillation - which means the heart beats in a bad rhythm - was similar to a heart attack.
Stress related
He said ventricular fibrillation of the heart in racehorses could be stress related and adrenalin could play a role.
He also said the death could have been caused by a by a large blood vessel like the aorta or a major abdominal vessel rupturing and bleeding out internally.
After Tuesday's incident, the Coalition for the Protection of Racehorses called on the racing industry to ban whips.
But Dr Stewart said excessive whipping wasn't a factor in Admire Rakti's death.
Jockey Zac Purton rides Admire Rakti out of the mounting yard to the race. Photo / Getty Images
He said Racing Victoria reviewed footage of the race and the jockey stopped using the whip when the horse didn't respond.
"The jockey immediately put the whip away and relaxed on the horse to ease distress," he told ABC Radio.
'There's no question in this case that the whip played any role whatsoever.'
Seven-year-old Admire Ratki's demise was a personal tragedy for Zac Purton, who had ridden him to victory at the Caulfield Cup only last month.
The jockey deliberately slowed down when he realised the horse was distressed in the latter stages of the race and they eventually finished last.
"The whole way through the run I thought I'd win," he said. "I didn't think they'd beat me from where I was."
With 800 metres to go the horse was not responding and Purton began to have suspicions all was not well.
Purton eased him down and virtually walked him over the line, 25 lengths behind the second-last horse, 200-1 outsider Mr O'Ceirin.
"I didn't know it was as bad as it was. I'm just shattered," he added. "He gave me such a great thrill there at Caulfield."
Admire Ratki's Japanese owner Riichi Kondo was also distraught. He was seen outside the stables after the horse's death where the body had been screened off by a green tent.
Staff put up tape and asked the public to move away from the area, saying "there is nothing to see here".
The reason for Araldo's demise was immediately clear. His trainer Mike Moroney said that the stallion had become distressed by a big flag and run off.
"It was a freak accident," he said. "They run the Melbourne Cup for 154 years and nothing like that has happened."
The deaths of the two horses has prompted an outpouring of comment online and reaction from animal charities who insist that racing is a cruel sport.
An RSPCA spokesman said Admire Rakti's death was a stark reminder of the risks to racehorses.
"Sadly, injury and death are the price some horses pay for our entertainment in a sport that puts intense pressure on animals to perform to the limits of their endurance."
WATCH Protectionist wins Melbourne Cup
Coalition for the Protection of Racehorses spokesman Ward Young said about 125 horses had died during or shortly after Australian races in the past year. "These events are more common than we would like to believe," he told AAP.
Donna Wallis, from Knorrit Flat, NSW went to see Admire Rakti before he raced at his pen in The Stables.
She said: "He seemed fine - a bit excitable. It's a real shame - very sad. He was fine in the race. It seemed to be when they got him back to the stables."
Sudden - and very sad
Kathline Gontin, from Kensington, Melbourne, also went to see Admire Rakti before he raced. She said: "He was a beautiful horse - I put a bet on him. I saw him walking (in the stables circle) after he had finished.
"He seemed ok. Just a bit excited. I saw them putting a stick in his mouth - I don't know why. Then after I left I heard he had died. It is so sudden - and very sad."
Admire Rakti, winner of the Caulfield Cup in brilliant style last month, raced near the lead for most of the 3200-metre journey.
Before the Cup, some experts predicted that Admire Rakti would struggle to run the 2 mile distance due to his heavy weight.
The analysts forecast that the stallion, at 58.5kg, would find carrying his weight at a fast pace over the long distance problematic.
No Cup runner weighing 58.5kg or more has won the race since 1975.
Winner Protectionist was the first German horse to gallop to victory at Melbourne, heading Red Cadeaux and Who Shot Thebarman down the stretch.
The 5-year-old stallion's owners will pocket A$3.6million of the Melbourne Cup's A$6.2million pool.
- Daily Mail Australia
