My first Cocker was diagnosed with a heart murmur when he was 9 or so and then with heart failure a few years later. Despite that, and with the help of some low dose medication, he lived until almost 17 with no further heart problems. His one and only symptom was getting a bit breathless and coughing out on a walk on a very windy day, which is what prompted me to take him to the vet in the first place.
Apart from his medication all I ever did was to make sure he stayed slim and fit, although everything went a bit saggy in the last year or so of his long life!
Have they asked you to take Orin back for a check up in a few months or are they leaving it to you to monitor him? Either way, the vet obviously doesn't think it's a big problem at the moment, and hopefully it will stay that way. My old boy's murmur didn't get worse as he got older.