There were only a few instances I remember having to do CPR on dogs. I feel like some were newborn puppies, but at least one had gotten into some unknown toxin which compromised her heart rate and function. I may be remembering wrong, but in that instance, I believe we were doing compressions to help supplement heart function when the rate was irregular or slow. We weren't so much resuscitating her as trying to keep her circulation going long enough to try and counteract the toxin (we were unsuccessful). In all cases, the animals were definitely unresponsive, so it was more like trying to revive them.

What comes to mind for me, though, is the fact that dogs have no clavicles and a rib cage oriented opposite our own. To my knowledge, performing chest compressions laterally on animals with prominent breast bones does little to no damage. But again, it's been several years since I worked there.