
My last dog had a very slight heart murmur picked up after a severe infection when he was about 15 months old. It never bothered or affected him in the slightest, he lived until nearly 14 and never needed any medication or treatment for it. I think in very small puppies often the flow of blood through their hearts can mimic a murmur and as Barbara says by the time she goes for her booster it will have disappeared (certainly the case with my human daughter :-D )
Found this bit too:
Many puppies are born with a slight heart murmur (or puppy murmur) that clears up by itself after 4-6 months. In many cases, vets will simply recommend a later checkup, just to be sure that the condition has resolved itself.Make sure you get proof that it has cleared for future insurance purposes
Hope you enjoy your new puppy - sounds like you have found a good breeder