This is horrible! Vets should be more careful with people's pets!
This is similar to how I lost my first cat, Sydney. He had kidney stones and needed an operation. The vet gave him general anesthesia and Sydney's heart stopped. As it turns out, the vet gave him more than he should have.
It's so hard to lose a pet that you love, and it's even worse when it is the result of a veterinarian's carelessness.