Some horse racing trivia... So, have any of you read about the X-Factor heart in horses? X-factor refers to a large heart gene only passed on through the x-chromosome. The larger the heart, the more oxygen a horse can pump through it's blood when it runs, making it capable of running faster. Sires cannot pass it on to their sons, only their daughters. Secretariet is known to have had the x-factor and had HUGE heart. He is one of only a few who actually had his heart weighed after he died. I can't remember but it seems it was something like twice the size of a normal heart. (Don't quote me). He was not a great "stallion" sire, but his daughters were highly sought.
Here is some info if you horse racing fans would like to read. I love to study horse pedigrees and this is very interesting...
Chasing the X-Factor, Unofficial Thoroughbred Hall of Fame