As is tradition for this 3-mile steeplechase - the highlight of a day of races at Nashville's Percy Warner Park - Arcadius, with jockey Brian Crowley in the saddle, trotted up the hill for everyone to see and to photograph after winning the race.
Then the horse returned to the champion's cooling station near the finish line and suddenly collapsed.
As 25,000 spectators strained to see what had happened, veterinarian Doctor Monty McInturff and two colleagues rushed to the side of the fallen horse.
"We got to the scene and his blood pressure was going quickly," said McInturff, whose crew took their emergency vehicle and supplies to the finish line to tend to the fallen horse.
"He went very quickly," despite the fact an IV and medication was administered.
Arcadius had already won a race this season in preparation for the 71st running of the Iroquois, which annually draws the top steeplechase horses, jockeys and trainers from all over the United States, Ireland and England.
McInturff said the horse did not die of heat stroke, for it was misty, 70-degree jacket-wearing weather.
"Arcadius had a pulmonary aneurysm. After the race, the artery (in his heart) ruptured," he said after speaking with the state pathologist who had examined the body.
Steeplechase is raced on a turf track with barriers such as fences to ditches the horses must jump.
While tracks like the home of the Iroquois have added breakaway fences and made many improvements to make the races safer for the horses, McInturff said nothing could have been done to save this horse.
McInturff's Tennessee Equine Hospital has served as a emergency medical team at the Iroquois steeplechase for 25 years. He said he has seen horses die before.
To see Arcadius die after earning its $90,000 cut of the $150,000 purse was heartbreaking, he said.
"He was the best horse of the day," said McInturff. "He honestly showed no signs of distress during the race. He won the big one. The horse ran beautifully. It was amazing to watch."