My son has a heart murmur and had a hole in his heart(repaired this past October)..actually I'm not quite sure if his murmur went away now that he no longer has a hole,..regardless the cardiologist told me that the murmur itself means nothing bad, will not cause him any issues, will not stop him from doing anything at all.
If you have other issues causing the murmur that's another story.
My son does need to take antibiotics if he has dental work done, but as of April 12, 6 months from his procedure he will no longer have to.