The current AHA/ACC guidelines no longer recommend antibiotics prior to dental and other procedures fro people with murmurs and heart valve problems to prevent endocarditis. The one exception is for people with prosthetic heart valves. I recently re-read the revised guidelines. I had a colonoscopy last week...which resulted in a single plolypectomy...and, of course, the new guidelines do not require pre-meds for these sorts of procedures so I have not been doing pre-meds since the guidelines changed.
They make a strong case for the revision. The primary argument is that so few cases of endocarditis are actually prevented by pre meds that the benefit is out weighed by the down side effects, e.g. the development of resistant strains of bacteria, cost, etc. Of course, if you are one of those who gets endo then their arguments don't help much.