There are many different kinds of murmurs. most of which don t cause any problems. The dentist was looking out for one particular variety caused by a mitral valve prolapse. This particular kind of murmur is caused by the a leaky valve between your left atrium and ventrical, and is sometimes hard to hear. If you have a very mild prolapse, or leaky valve, it may not even always be present for a doctor to hear. Other murmurs seem to be just the noise made when the heart works, and nobody really knows why. You echo will detect if there is some defect which causes the murmur and the extent of the defect if present. If it is really mild, then likely the dentist will just want to have you take antibiotics prior to the surgery and monitor your heart during the procedure. Even if they find a prolapse, as it hasn t caused you any problems so far, it isn t likely to in future. A lot of folks with MVP don t realize it until a dentist or student doctor with exceptionally keen hearing detects the click. Even then, others won t hear it at all. If you have one, it will need to be monitored periodically, but your GP will tell you how often. Usually it s a once a year or every other year listen and sometimes either an echo or 24 hour monitoring. Nothing to get too worked up about either way. Your dentist is just being cautious on the good side. Sign of a good conscientous dentist.