That comes as no surprise to Ontario Veterinary College professor Dr. Peter Physick-Sheard, who has been studying how equine hearts function in his research with some other equine athletes โ€“ Standardbred racehorses. โ€œI tell my students that if the horseโ€™s heart is beating steadily like a metronome, step back โ€“ because he might fall over on them,โ€ Physick-Sheard says. Irregularities in heart rhythm are normal in horses; hearing lub dub, lub dub, pause, lub dub is perfectly natural. However, there are some types of irregularities that can cause concern.

Physick-Sheard explains that each contraction or beat of the heart is preceded by electrical activity initiated in a special area of the heart (called the pacemaker) triggering biochemical changes that signal the heart muscle to contract. ECGs (electrocardiograms) detect that electrical signal. โ€œEvery wiggle on the ECG screen means a cardiac contraction,โ€ explains Physick-Sheard. The data from an ECG can also indicate whether or not the heart muscle is healthy or whether the heartโ€™s internal conduction system is normal, and can provide other information about heart function.

The Wide Range of Normal

Itโ€™s important to know what normal heart rhythm looks like in a horse to help diagnose and treat problems when horses are not healthy. โ€œWhat weโ€™ve learned is that variations in heart rhythm donโ€™t necessarily mean disease, and disease is not necessarily associated with variations in heart rhythm,โ€ he explains. โ€œThe normal variation is huge. Itโ€™s absolutely normal for all horses to show some rhythm disturbances day to day. In fact, an absolutely steady, regular rhythm is abnormal.โ€

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