Do you know why a Thoroughbred can deliver that great burst of speed to eat up a mile in 1 1/2 minutes, or how an endurance horse can maintain the strength and stamina to cover long distances at steady speeds? Of course you do: Conditioning. Conditioning builds sturdy bones, develops strong muscles, and maximizes efficiency in the cardiovascular system. Although all these components are needed to deliver peak performance, like a souped-up engine that drives the sports car, it’s the “tuned-up” heart that drives the athlete, and makes everything else happen. That’s because the amount of oxygen required by muscular tissues is extremely high during exercise compared to rest. It’s the heart’s job to increase delivery of blood during exercise in order to meet those high oxygen demands.

What this mighty organ can do is amazing. When a horse is at rest, the heart pumps about 10.6 gallons (40 liters) of blood per minute; during maximal exercise, a conditioned heart can pump 79 gallons (300 liters) a minute. (Compare that to the comparatively meek human heart, which only manages to move around 1.0-1.3 gallons, or four to five liters, per minute at rest.) During exercise, the equine heart can increase from around 35 beats per minute up to a whopping 240 beats per minute! And yet, this organ only constitutes about 1% of the horse’s overall body weight, coming in at 3.3-8.8 pounds (1.5-4 kg).

Anatomy of a Heart

The heart’s purpose is to act as a mechanical pump–squeezing blood out of the heart to the lungs, where it takes up oxygen, and from there to the body to provide nutrients and oxygen, says Daniel F. Hogan, DVM, Dipl. ACVIM, an assistant professor of cardiology in the Department of Veterinary Clinical Sciences at Purdue University and a researcher in equine cardiovascular disease