Hi Steph,
Both of my sons have heart murmurs. My 4 month old was diagnosed w/ a heart murmur when he was 2 months old. An echocardiogram was performed and he was diagnosed w/ Pulmonary Valve Stenosis. Currently it is mild but needs to be checked every 6 months (only because of his age). The cardiologist said that many people have hear murmurs and don't know it or have any symptoms. If my sons' murmur stays mild, no restrictions or treatments will be necessary. He will however need to take antibiotics prior to any dental, bladder, or colon procedures to prevent infection of the heart valves.
Recently a heart murmur was also heard on my 3 year old for the first time. The pediatrician said that it was an "innocent heart murmur" which is very common with children. Perhaps this is what your doctor meant by a "floating heart murmur". Here is a link http://familydoctor.org/453.xml. While I was pregnant w/ him a fetal echocardiogram was performed and no heart abnormalties were detected. Therefore I'm not very concerned about the heart murmur but will continue to ask about it at his yearly check-ups. If I notice he appears to have shortness of breath or seems more fatigued than normal (either at rest or play) then I'll request an echocardiogram immediately.
Good luck at your daughters' follow-up and if heart disease or defects run in the family (it does for me) be sure to let the doctor know. If you're really worried (it's hard not to - I know) ask about an echocardiogram or an EKG (ECG). Best wishes - S.