An exceptional heart

When a routine prepurchase exam turns up an unusual cardiac condition, a mare defies the textbooks by thriving.

If not for a prepurchase exam, no one would have known there was anything unusual about Frosty.

The 7-year-old Quarter Horse mare is deaf, a congenital condition linked to her extensive overo pattern, but that is not remarkable. What sets Frosty apart is that she is able to carry a rider and romp in her pasture like any other horse despite having a cardiac condition that, in theory, should greatly limit her activity if not lead to congestive heart failure.

“The cardiologists are scratching their heads with this one,” says Philip Johnson, BVSc, of the University of Missouri. “Frosty isn’t following the typical pattern of what we’d expect to see. Obviously, she hasn’t read the textbooks.”

Frosty was a homebred foal, born in 2008, produced specifically to be sold. “We owned her mother, who had distinguished Western pleasure lineage, and her sire was a world champion halter producer,” says Johnell McLean of De Soto, Missouri. “We were hoping to produce an all-around horse that we could sell the following year.”

But the timing couldn’t have been worse. The economic downturn of 2009 hit the horse industry hard, and no buyers appeared for the yearling. Fortunately, McLean was perfectly happy to keep the filly at home for a few more years. “We were in no rush,” she says. “She’s a great mare to work with.”

Frosty was trained to respond to visual cues and was eventually broken to ride. She was shown successfully in both halter and Western pleasure classes. Eventually, the market picked up, and in the spring of 2015, a buyer emerged who was interested in putting Frosty to work on a cattle operation, riding fences and checking calves.

As a routine part of the transaction, the buyer arranged for a prepurchase exam at the clinic of Frosty’s veterinarian. “Frosty had had regular veterinary care her entire life and had always been healthy,” McLean says. “So we weren’t anticipating finding anything usual. The prepurchase exam was just a formality; the buyer had even already made shipping arrangements to pick her up afterward.”

However, one of the first things the