According to a group of researchers from the United Kingdom, heart murmurs are common in athletic horses, but do not negatively impact racing performance.
"A high prevalence of heart murmurs is known to exist in horses," explained Lesley Young, BVSc, PhD, DVA, Dipl. ECEIM (European College of Equine Internal Medicine), DVC, MRCVS, an equine cardiologist and lead author on this study. "Until this study, however, the effect of these murmurs on the performance of athletic horses was unclear."
Young and her colleagues hypothesized that horses with heart murmurs would have poorer athletic performance compared to horses without murmurs.
In this study, 526 Thoroughbred racehorses were evaluated by cardiac auscultation (veterinarians listened to their hearts using stethoscopes) and color flow Doppler echocardiography (ultrasound imaging of the heart) on one or more occasions.
The presence or absence of a heart murmur was then compared to the published race times for each horse.
"Our data showed no significant relationship between racing performance and the presence of a heart murmur in any type of racehorse included in this study." –Dr. Lesley Young
As predicted by the authors, there was a high incidence of murmurs in the population studied--as many as 45% of the horses were affected in some groups--and the number of horses with heart murmurs increased with age and time in training.
However, "our data showed no significant relationship between racing performance and the presence of a heart murmur in any type of racehorse included in this study," said Young.
The authors concluded that this study supports the school of thought that, in most cases, heart murmurs in athletic horses are related to normal adaptations of the heart that occur with exercise and are not related to a heart abnormality.
The study, "Heart murmurs and valvular regurgitation in Thoroughbred racehorses: epidemiology and associations with athletic performance," was published in the Journal of Veterinary Internal Medicine in March 2008.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.