Size matters in matters of the heart of an elite horse athlete.
Taking a sample of 34 Arabian horses, 23 of them highly successful in endurance competitions, researchers at the University of Pennsylvania used an echocardiograph to measure the horses' hearts.
The star jock horses had larger left ventricles. A bigger heart offers an advantage to the horse -more blood is being pumped into the muscles during exertion.
Other studies have shown similar findings in Thoroughbred and Standardbred racehorses.
What researchers are wondering now involves the old nature vs. nurture question. Were the big hearted horses that became great athletes born that way, or did their hearts get bigger thanks to lots of cardio exercise?
More testing is necessary. It will be difficult to conduct these tests. Many many horse hearts will have to be measured before and after they become (or don't become) successful competitors. Not only that, many horses begin extensive training before they are fully grown. A not fully grown horse probably does not have a fully grown heart.
Still, it is a question to run with.