Everyone will have a different opinion on this but I tell you what I would do, mostly based on the age (10 yrs) for your dog.
My goal would be to do the best to keep him as healthy and comfortable as I could. And major heart surgery would NOT be on my radar. At that age, the surgury could easily kill him, recovery would be rough, and no assurance that would add any extra time either.
So I'd go to specialist to make sure the testing was as clear as it could be NON-invasively so I would have a better grasp on what was going on. Then I'd use the appropriate meds to keep him as comfortable as I could.
There are also holistic vets that I know do amazing things to keep our dogs comfortable. So you may want to look at that also.