Is there a link between flossing and infective endocarditis?

Yes, per current inf: Current info does substantiate such a periodontal cardiac relationship. Flossing is important in maintaining proper periodontal health.

Has not been proven: Interesting question. There has been speculation linking the two, with the idea being that bacteria sent through the blood stream could wind up colonizing on a remote surface, such as a heart valve, but to date it has never been proven that this occurs. I'd keep flossing and keep those teeth and gums as healthy as possible. It's good for your general health.