If I remember correctly, heart murmers are typically caused by either heart injury, or by genetics. With the kitten obviously being so young, it would probably be safe to assume that it wasnt heart injury that caused the murmer, it was likely heriditary from its parents. The good thing is, being he is young, hopefully he will grow out of it as his body matures. It wouldnt surprise me if the vet recommends making sure there is adequate taurine in the diet, since it does play a role in heart development for growing kittens if I remember correctly.
Shengmei, out of curiosity, how do you know that the excess taurine and dandelions were helping with the murmer? If it was improving, how do you know what was improving it? Just like you used to always say how you didnt like Innova because "it gave your cat a heart murmer", im wondering how you come up with the concrete evidence.