Source: http://www.si.com/longform/belmont/index...

In waging the most glorious Triple Crown campaign ever, Secretariat made racing history in 1973. In the doing, he took the author on an unforgettably exhilarating ride.

“We were all shocked,” Swerczek said. “I’ve seen and done thousands of autopsies on horses, and nothing I’d ever seen compared to it. The heart of the average horse weighs about nine pounds. This was almost twice the average size, and a third larger than any equine heart I’d ever seen. And it wasn’t pathologically enlarged. All the chambers and the valves were normal. It was just larger. I think it told us why he was able to do what he did.”