Trainers have often believed that heart size has played a huge role in racehorse performance. As science improved it has been proven to be true. I won’t go too much into the science of it all, but will give you some examples.In Thoroughbred horses, heart mass is roughly 1% of overall body mass. This means most TB’s have a heart mass of 4-5kg. In other breeds the heart mass is less than 1% body mass. However, some famous racehorses had very different heart sizes:

Secretariat, 1973.

Famous for winning the American Triple Crown with incredible style. He had a heart mass >10kg.

Secretariat. Credit, Secretariat’s Meadow.

Sham, 1973.

Secretariats only true rival for the Triple Crown and one of the best horses of the time. He had a heart mass of 8.2kg.

Sham. Credit, Horse racing Nation

Key To The Mint, 1972.

American Champion 3 year old and brilliant Broodmare Sire. Had a heart mass of 7.2kg.

Phar Lap,

Famous Australian racehorse. He had a heart mass of 6.4kg,

Phar Lap

This is not an extensive list. There are so many other world famous racehorses who may have also had larger hearts, including: Red Rum, Seabiscuit, Arkle and Man O’War. It may be that there was never an autopsy so no record of their heart size. But wouldn’t it be interesting to find out?