[OwnedByJezebel]

If the vet never informed you about pre-surgical blood tests, then the vet might bear some responsibility for this. On the other hand, depending on what caused the heart attack, it may have been something that blood tests couldn't detect. Have you discussed this with them?

I can't imagine what they could have had to do to get the bill up to $5,000. What exactly have they done over the course of 4 days that amounted to that? Look into Care Credit, if you are approved you can pay it off over a year or two, interest free.