No one wants to hear that their horse—be it a weekend warrior or a high-performance equine athlete—has a heart murmur. But there’s some good news on this front: While, yes, some heart murmurs are bad news and can spell the end of a horse’s riding career, others have little to no impact on equine athletic pursuits. The trick is determining which kind a particular horse is afflicted with.

At the American Association of Equine Practitioners’ Focus on Poor Performance meeting, held Sept. 10-12 in Lexington, Kentucky, Sophy Jesty, DVM, Dipl. ACVIM, reviewed heart murmurs and their effects on equine performance. Jesty is an equine cardiologist based in Charleston, South Carolina.

Murmurs 101

Before delving into which heart murmurs are clinically significant and which are just noise (that should be carefully monitored, of course), Jesty went over a few basics with attendees.

She explained that murmurs can be physiologic (meaning they’re benign flow murmurs) or due to three categories of cardiac pathology:

  • Shunt—An abnormal pattern of blood flow in the heart;
  • Regurgitation—When blood flows backward from the lower to the upper heart chambers; or
  • Stenosis—When a heart valve constricts or narrows.

“Valve regurgitation is the most common cause of murmurs in horses, congenital heart disease can cause murmurs in horses but is less common than acquired degenerative valve disease, and valve stenosis is rare,” she said.

Jesty said practitioners grade heart murmurs on a six-poi