Oops , my cat Sydney had a heartmurmur too. He was diagnosed with "Feline Hypertrophic Cardiomyopathy". The vet decided to wait 6 months before giving him medicine; but unfortunately, he died of a heart-attack 3 months later... . I am glad to read that Tux gets medication already!
I hope I didn't scare you to much, but this is a serious heart-condition