Stray cat - heart murmur

Last month I rescued a stray cat that showed up at my door. He had clearly been outside for a while as he was in rough shape. Cauliflower ear, heart murmur, broken tooth. The vet determined he is roughly 12 years old. I love the little guy and have been fostering him since.

The vet checked his heart with a stethoscope while at the shelter and said he had a grade 4 heart murmur. This could’ve been from the stress of being in a cage at the shelter for a few weeks. We have not checked his heart since.

Tomorrow he will go under anesthesia to remove the broken tooth but the foster said there is a chance he may not make it and while I know theres always a risk, im so nervous.

My questions are: has anyone gone through this and can give any advice? I think the vet is going to do an ultrasound tomorrow before surgery however, what other tests can I ask the vet to run?

I don’t want to put him under surgery if there is something that can be done to lessen his murmur and we do this surgery at a different time. Please advice