Client education needed
Dr. Marianne Sloet and colleagues at the Department of Equine Sciences of the University of Utrecht in the Netherlands looked
at a number of horses during a five-year period and assessed the murmurs that were found at prepurchase examination or at
long distance rides.4 They found that only 10 percent of the horses that had heart murmurs experienced reduced performance but that the presence
of murmurs still affected the sale price of many of the horses.
During the study period, Sloet's team found murmurs in 62 horses at prepurchase examinations and in 15 horses competing at
distance rides. Complete cardiac examinations were performed on these horses. Seven percent of the murmurs were loud, and
there was good correlation between heart auscultation with a stethoscope and more in-depth echocardiography results in 68
of the 77 horses. Mitral valve problems were found in 63 horses, and tricuspid valve issues were noted in 40 (some horses
had multiple problems).
The researchers did find that the left atrial diameter (LAD) was the most important feature to predict future performance.
The heart's left atrium increases in size as blood leaks into this chamber through a compromised mitral valve. Over time,
the wall becomes thicker so it can try to fully eject the volume of blood building up in the atrial chamber because of back
pressure and a leaky valve. LAD in normal horses should be less than 14 cm. If LAD is normal in the presence of a heart murmur,
then the flow problem is being well-tolerated by the equine heart and shouldn't cause performance concerns. If the LAD is
increased, the heart is adapting to the pathology in the valves, and the horse must be removed from performance and carefully
Forty-three percent of the horses in Sloet's study sold for the original asking price, despite being identified as having
a murmur; 21 percent sold for a lower price because of the presence of a murmur, and the sale was terminated in 36 percent
of these cases. The team concluded that the perception of heart murmurs was such that clients viewed their presence negatively,
despite overwhelming evidence that less that 10 percent of horses with murmurs demonstrate clinical significance.
Equine clinicians are in a unique position to be able to educate clients and horse owners as to the possible significance
of murmurs and to perhaps clear up some of the confusion as to their importance.
Dr. Marcella is an equine practitioner in Canton, Ga.
1. Kriz NG, Hodgson DR, Rose RJ. Prevalence and clinical important of heart murmurs in racehorses. J Am Vet Med Assoc 216(9):1441-1445.
2. Zucca E, Ferrucci F, Stancari G, et al. The prevalence of cardiac murmurs among standardbred racehorses presented with poor
performance. J Vet Med Sci 2010;72(6):781-785.
3. Young LE, Rogers K, Wood JL. Heart murmurs and valvular regurgitation in thoroughbred racehorses: epidemiology and associations
with athletic performance. J Vet Intern Med 2008;22(2):418-426.
4. Conference on equine sports medicine and science, Saumur, 2002.