So many people responded to my recommendation of "Pure Heart" by William Knack regarding his experience with Secretariat, I thought I would also recommend the book where I read the story. Sports Illustrated always had great writers, and this is by their best.
For anyone who enjoys great sports riding, I recommend:
Fifty Years Of Great Writing: Sports Illustrated 1954-2004
More than 50 of the best articles from sports illustrated writers, including "pure heart" by William Knack, an unforgettable story about Secretariat.