Several years ago DH and I went on a cruise and as it happened the man in the couple who dined with us had a mechanical valve. Apparently he had a hunting accident (he was shot) and that resulted in the valve needing to be replaced (I didn't ask for details). At any rate, he started out taking warfarin, but after awhile "didn't see the point" (or something along those lines) and took himself off of it. Nathan and I were both shocked. Of course, he seemed like the type that would play Russian Roulette if given the chance too.