Mitral valve regurgitation is a cardiac condition where the heart's mitral valve does not close tightly and therefore blood can flow backward in your heart. If the blood is not moving through your heart and to the rest of the body properly, you can feel fatigued and short of breath. In mild cases, no treatment is necessary. It depends on the severity of your signs and symptoms. Mitral valve regurgitation is more common than you may realize and most are untreated. Treatment is up to your cardiologist. If you don't feel comfortable with his decision to not treat, then I recommend getting a 2nd opinion to ease your mind and be sure. You can bring your medical records and films to another cardiologist for review. Treatment is based totally on the progression of the disease along with the symptoms. But you should be monitored regularly with doctor visits. That is the key. Look at the website below for info and if you click on the red highlighted words you can find out more details.
Concerning the use of antibiotics before dental visits, not all docs are doing that anymore, so again, it will be up to your doctor.
I wish you well!