Lost A Good Cat Today

I'm a dog person but my sister has cats. I can appreciate the way these pets work their way into our hearts no matter what they are...Cats, Dogs, pot belly pigs, whatever.
We have always had to take our dogs into the vet for their final visit, we've never had one pass-on at home. I don't know which would be more heartbreaking. Taking them in brings sadness and guilt. I can only imagine that finding that one passes on at home is shock instead of guilt.