I've seen thumps (aka Synchronous Diaphragmatic
Flutter (SDF)).
I've had two horses to whom it happened to.
One, 110 degrees and a hundred miles at the Four Roses
Ride. It was just a hard day, too much heat, too many. He was a
"fit" horse.
Second time, my horse did the Big Horn 100 and then we
trailered out to Tevis and got pulled for "thumps" at Deadwood. I asked to
much of him. I rode him beyond the level of his conditioning.
