Let’s say you’ve decided you want a particular breed of dog but you’ve never been schooled in how one goes about these things. You haul yourself over to the nearest pet shop and fork over the proceeds from your new job’s first check. And you’re happy with yourself—you love your puppy.

Fast-forward three years later and you still have that new job—at the vet hospital. You know a whole lot more about what it takes to find a great pup and so you know you did it all wrong the first time. Somehow, your dog (a yellow Lab) has so far managed to escape all major breed-related crises, in spite of her puppy mill origins.

You breathe a sigh of relief every time something goes even a tad wrong with her and you fear the worst…but it turns out to be nothing.

Then you notice something a little odd. Every time you take her for a long walk or a romp in the park, she seems to get tired faster than all the other dogs. You always let her rest and recover before heading home—and she’s always fine. You chalk it up to the Miami heat and her laziness.

One day, though, she collapses after a run. You wet her down and rush her to the hospital only to find that her temperature’s still over 104. What must it have been when she collapsed?

Looks like a classic case of heat stroke. Her temp comes back down nicely and all is well. Her bloodwork is normal. Her EKG is normal. No funny airway problems in evidence. She checks out just fine.

But you tell your vet about the other times she got tired. So after a week of rest, you bring her in to work and run her around out back. Lo and behold, her temp gets up to almost 105 within a few minutes.

You scratch your head. Your vet scratches her head. Her memory calls up a few strange diseases from waaay back when she was a vet student—but they’re really fuzzy. So she calls the internist, who remembers something, too, though a little more clearly: exertional myopathy, defined by one of a variety of muscle-related diseases most commonly found in Labrador retrievers. Bingo?

Time for some tests. Blood samples looking at lactate levels before and after exercise and muscle biopsies are in order. (We start with the blood tests first—they’re less invasive and less expensive.)

Your vet is so pleased to have determined the general cause of your dog’s problem (though the results are still pending) but you can tell she’s trying hard not to act excited about finding a zebra after hearing what should have been a horse’s hoofbeats.

After all, this is your dog—and the expected diagnosis means your dog won’t be going to the park anymore. She’ll be sitting inside in the AC getting fat and lazy. You want more for her than that. This sucks.

Still, it could’ve been worse. It could’ve been a cardiac problem, you tell yourself—a lifetime of medication and a slow decline into heart failure, with all its attendant expenses. It could’ve been some other bizarre and progressive neuromuscular disease—ditto the deterioration and financial hardship. It might even have gone undiagnosed—and one fateful day she might have died at your feet in the park.

So you count yourself lucky and resolve yourself to a lifetime of counting calories instead of romps in the park. She’ll be your own personal couch potato. It’s more than what other dogs in her paws ever get, you rationalize. And it could have happened to anyone’s dog.

Still you wonder: What if she hadn’t been bred at a farm where her brother was more than likely her father? Hindsight’s 20-20…and it’s often a bitch…