Secretariat’s time in the 1973 Kentucky Derby set a record that still stands: 1 minute 59.4 seconds. But few people realize he was actually accelerating throughout the race. His successive quarter-mile times were 25.2, 24, 23.8, 23.4, and 23 seconds.

On autopsy, it was discovered that his heart weighed 21 pounds, three times the size of a normal horse’s.