If you have been diagnosed with, say, symptomatic MVP (Mitral Valve Prolapse) or another heart condition, the ADA's guidelines do recommend antibiotics prior to and following dental procedures.

I also think that getting a second opinion would be a good thing to do, but without telling the second dentist what the first one had stated. If the opinions match, then, you'll, at least, have a choice of who you want to see for treatment(s).