Have you known a dog with heart disease go under anaesthetic?

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My Cavalier has to have X-rays done in 2 weeks so needs anaesthetic (and then maybe an operation). She has heart disease that has got progressively worse and I don't know her chances of pulling through. The vet won't do anything that isn't absolutely vital (e.g. dental work) because of her heart trouble. When I asked the chances of her not waking up after the anaesthetic with her heart condition he just said 'there are risks'. Do you know a dog who has had bad heart disease and gone under anaesthetic? Did they pull through ok or not? I want to know just how risky it would actually be. I was talking to a lady in the vets the other week and her Cavalier died under anaesthetic because he had (undetected) heart trouble. How high is the risk? Regardless, I need to take the chance because my dog is in pain and I can't let her suffer. I just want to be prepared for the worst. Thanks xx