Alot of puppies of all different breeds can suffer with minor flow murmers
that DO disappear once they reach 16 weeks of age.
Even if they persist there may be no cause for alarm if they are quiet.
If you are unduly worried there are vets around the UK that do specialise
in Cardiology.
In my own breed Boxers there is a heart-testing scheme for all Boxers
and they put controls in place that ideally no dogs should be bred from
unless they were heart-tested and graded a zero or one. (stethascope examination) We are lucky as most of the breed clubs arrange to have a cardiologist present at their open/champ shows and the fee for testing is £7.50 per dog. Todate the scheme has been running over 10 years and
over 5000 dogs (Boxers) have now been tested. The incidence of serious heart murmurs in Boxers is decreasing, so the control scheme does work.
Wishing you all the best with your puppy and hopefully it will just turn
out to be an innocent puppy flow murmur that disappears

Kindest Regards
Kirstine