Here's the bit I don't trust: Tests show they are perfectly normal, with no brain damage. OK, the tests could have been excellent, but do they measure what you'd want to know?
How can you tell whether higher brain functions were damaged? Afaik, it took them years to figure out that heart-lung machines were causing brain damage, and that was with people. I may be unfair about this--I'm going by what seemed like a tone of faint surprise in news reports from a year or two ago. Maybe they'd suspected brain damage for a very long time, but only proved it more recently.
With a dog, I suspect that the only way to have a chance of telling would be to have a longterm pet, preferably one that was doing obedience trials, herding, and/or frisbee-catching get chilled. The results wouldn't be double-blinded, and might be too subtle for formal measurement. And that isn't the sort of dog you use for experiments.
What I can't figure out is that there are artificial hearts which work reasonably well--no substitute for an actual heart, but they can keep people alive for months, and they don't cause brain damage which measurably increases by the hour. The current theory seems to be that the problem with heart-lung machines is the heart part (problems with filtration? and with getting the right sort of pressure). I wonder why they don't use implantable hearts as a model.