Is there much of a link between flossing and/or using mouthwash and infections of the heart valves?

No.: Antibiotic prophylaxis is only recommended for dentist treatments, and then only in certain heard conditions.

No: Endocarditis can be caused by extensive dental work where bleeding is likely and bacteria of the mouth can gain access to the vascular system. Flossing usually does not cause bleeding but if so the amount of bacteria released into the blood stream is negligible. Most endocarditis occurs in previously damaged heart valves.

Perhaps.: Good dental care greatly reduces the risk of bacteria getting in the blood stream from the mouth, but this is likely something that occurs frequently in normal people. Abnormal heart valves are prone to infection so procedures that are likely to cause bacteria entry into blood are hazardous. Flossing is very low risk. Some dental procedures and colonoscopy may require antibiotics for safety.