re: Anyone given or heard of a dog given CPR successfully?

From a strictly medical standpoint, canine CPR is just as effective as human CPR. Which means it’s not very effective. Something like 7% of CPR on humans is effective. Largely because the American Heart Association gets money every time someone gets a card, their lobbyists have done a great job of getting mandatory CPR training written into all sorts of job descriptions. This has led to widespread misconceptions that CPR is a cure all. It doesn’t help that on TV they give CPR to a guy run over by a truck and five minutes later he is drinking a beer at the bar. CPR is meant for a fairly narrow set of medical conditions based around specific cardiac failures. For instance, all that CPR you see on gunshot victims. That shite doesn’t work. Your heart isn’t beating in that case because you have bled out. Manually pumping the heart isn’t going to circulate blood that isn’t there. Sorry but when you are out of blood you are dead.

All that being said, one of the conditions for which CPR absolutely does work is drowning. The heart has stopped because of a lack of oxygen and is subject to restarting once oxygen content is restored. Even better in your scenario is that the water was cold. The cold serves to protect brain function in the absence of oxygen. There are documented cases of bringing people back from cold drownings where they have been underwater for up to 20 minutes. The saying in the medical world is you aren’t dead until you are warm and dead.

So, yep, you killed your buddies dog.