I have a Cavalier, my Black & Tan, Hazel who has a grade 2 murmur. I have used supplements in the past but atm I’m not using any. Hazel has had her murmur since 2 months old (probably born with it) and she’s 6 years old now. I hasn’t changed yet. COQ10, Hawthorn, Taurine, L-Carnitine are good for the heart. I’ve given supplements for humans and made for dogs. Some of the ones made for dogs are: Cardio Strength, Bio Cardio, the supplement from Nature’s Farmacy (I think it’s called Heart Strength?). There’s also a site called Mainly Dogs that has one.
