Well i cannot say i have experience as such, but my cat Ash, the big grey one in my siggy, is coming up 12 years old and last visit to the vet, i was told he had a heart murmur, apparently they are graded, his is very low grade, however I was advised to do nothing, just keep an eye on it, on his last visit which was saturday just gone, the vet could not even hear it, so i am a bit puzzled, it does not mean he has not got one i guess, but the fact it has not gotten worse, or does not appear to be there is a good sign, i was told that cats with heart murmurs, especially elderly ones are prone to renal failure,but then that is quite normal for older cats anyhow, so worth keeping an eye on, but I have not been told to do anything, so IMO, if kitty seems ok and is doing well, and you keep a close eye on it, i would not go down that road, if it ain't broken don't fix it,come to mind, but would be good to get some further advice from people on PT who have been through this, as i said this is also new to me.,good luck.