Bob Judd, DVM, DABVP (Equine Medicine), DABVP (Canine and Feline Practice)
In general, the equine heart is a very healthy organ and is rarely a cause of disease. Horses don’t have human-style heart attacks but can have other heart issues.
When there is a problem, it can be serious, such as a fatal cardiac arrhythmia after exercise. In Italy in 2011 an Olympic gold medal-winning horse suffered a fatal aortic rupture. Dr. Celia Marr, BVMS, MVM, Ph.D., DEIM, DipECEIM, FRCVS, an equine internal medicine specialist based in Newmarket, Suffolk, states that the horse’s heart is well adapted to its role as an athlete.
A horse’s normal resting heart rate can be as low as 30 beats per minute but can increase to 250 beats per minute at a gallop. This means that at a gallop, your horse’s heart can pump over 60 gallons of blood per minute efficiently.
Your horse’s heart can have variable heart rates depending on what’s happening with the rest of the body, and this is normal. Many older horses and horses in athletic shape have long pauses between beats. This may make you think there is a problem, but in most cases, there is not.
The most common rhythm abnormality in horses is atrial fibrillation, an irregular and often very rapid beat, and unless you use your horse heavily, you may not even know it is present. Fortunately, horses do not die from atrial fibrillation and some horses will even self-correct the erratic rhythm. However, atrial fibrillation can be a cause of reduced performance and some horses require treatment.
Horses can have heart murmurs, and most are not serious. However, any horse with a significant murmur needs a cardiac ultrasound to find the location and severity. Fortunately, cardiac problems that lead to sudden cardiac death are rare in horses.