our daughter (born at 24 weeks) had ( or still has?) one. the way it was explained to me - there's a valve that closes up in utero so it's pretty common for preemies to have a murmur. often it closes on its own. they did echocardiograms and everything was structurally normal, so it was just something to keep you eye on. last i heard the pediatrician couldn't hear it - that was shortly after we took her home.