Today, the normal weight of a horse's heart is 8.5 pounds. Even though Secretariat's heart was not weighed at autopsy, Dr. Thomas Swerczek, head pathologist at the University of Kentucky, estimated it at 22 pounds after finding the second-largest heart in Sham (Secretariat's Triple Crown rival) and weighing it at 18 pounds.
"I have done thousands of autopsies, and I had noticed differences in heart size in horses before we did Secretariat," Swerczek said. "I had picked up the difference in the male and female hearts and noticed that some were bigger than others.
"But I didn't pay much attention until Secretariat came along. He was completely out of everybody else's league. Looking back at what he had done, it was easy to put a connection to it. The heart was what made him able to do what he did. It explained how he was able to do what he did in the Belmont Stakes – a mile and a half race (Secretariat won by 31 lengths in track-record time). You would have to have a large heart to do what he did. It would be impossible for a horse with a small heart to do that."
Recalling the moment Secretariat's heart was uncovered, Swerczek said, "We just stood there in stunned silence. We couldn't believe it. The heart was perfect. There were no problems with it. It was just this huge engine."