When it comes to the hearts of Standardbred racehorses, size does matter. Danish researchers recently published the results of an echocardiographic study in which they found that heart size correlated with athletic performance. However, "excellent cardiac function is only one of the important requirements to become a successful athletic horse," concluded the authors.

Heart size has long been believed as an indicator of talent in racehorses, and it has been shown that Thoroughbreds in training have hearts that are larger than untrained Thoroughbreds. The same is true in Standardbreds.

According to the Rikke Buhl, DVM, PhD, and other researchers at Denmark’s Royal Veterinary and Agricultural University, human studies using echocardiography (a test that uses high-frequency sound waves to image the heart and surrounding tissues) have suggested that athletic training might be associated with an increase in the size of the left ventricle (the lower left chamber of the heart, which pumps oxygenated blood out to the body) secondary to increased wall thickness, increased chamber diameter, or both.

The study, which appeared in the Journal of the American Veterinary Medical Association, detailed the study of 132 trotters (76 females and 56 males). The horses were all untrained 2-year-olds when the study began. The veterinarians looked at each horse’s heart four times at six-month intervals using echocardiography. They combined this information with data on training intensity and racing performance for the 103 horses that completed the study