When we first took Nell ( Lab) to the vet at nine weeks she was diagnosed with a heart murmur, the vet told us not to worry that it might go, but it didn't, Our breeder did offer to take her back, she has a grade two heart murmur, she's four now, and it doesn't bother her at all.
We don't treat her any differently than any other dog weve had, she gets at least three hours a day exercise, and runs like a greyhound
Nell is a realy hyper girl, and to restrict her in anyway wouldn't be fair to her, my vet agreed with me, up to now she has been fine, with no treatment at all
I'm sure there vet will advice them on the best way to deal with it, if the murmur doesn't go.