Do Heart Murmurs Affect Performance?

To understand the workings of a heart murmur, it is important to know how the heart operates in horses. The average sized horse has a heart that is the size of a basketball and it is the centre of the cardiovascular system. There is approximately forty-five liters of blood in the body of a horse that needs to be pumped by the heart. The heart pumps at an estimated rate of forty beats a minute and the valves that allow the blood to flood in and out of the heart causes the “lub-dub” sound that is heard through a stethoscope.

A heart murmur is caused by an abnormality of a heart valve, and the most common amongst horses is the aortic insufficiency murmur. The abnormality of the valve causes blood to be leaked back into the heart as soon as the heart starts to relax, and it is this flow that causes the disruption that is referred to as a murmur. Heart murmurs, unexplainably, are often found in performance horses, such as flat and steeplechase racehorses.

To confirm the suggestion that horses with heart murmurs perform less efficiently than horses with perfect health, Dr. Lesley Young, a leading equine cardiologist, decided to run a study to explore heart murmurs in thoroughbred horses. Researchers took five hundred and twenty-six horses that were racing fit and put them through various tests, including jumping and flat racing. The distances were varied between a thousand meters to six thousand four hundred meters and veterinarians were on hand to evaluate heart rates and performances, and to ensure the health and safety of the horses.

The study concluded that heart murmurs did occur in racehorses over time and with age, but was not as result of a heart abnormality but the heart making normal adaptations. Heart murmurs were also not effecting the performances of the horses, as first suspected. Cardiac testing and close monitoring has therefore shown that although heart murmurs do occur in athletic horses, their performance output is the same as horses without heart murmurs, and that exercise and not genetic faults are the cause of this condition. Racehorses are therefore more likely to be affected if they remain in training and racing over a long period of time, but they will still be able to deliver magnificent performances.