Chrystal:
Before my first flight post-op, I was anxious that someone would hear my heart valve and turn me in as a ticking timebomb <vbg>. However, no one heard ANYTHING.
I have flown many times since then, never had a problem, never had to show my St. Jude ID card. Am flying this weekend in fact and again next month. Also planning a trip to Reston VA in June for a convention.
Because your husband's on warfarin, he should be in a better situation than someone NOT on warfarin for a long flight like the one you describe. He may want to talk to whoever manages his anticoagulation therapy and see if they want him to be on the high side of his INR range. (I would do that if I were planning an overseas trip.)
You will need to watch yourself, too. You might ask your doctor if there's something else you can do other than just stretching your legs during the long flight. Don't know if taking aspirin before your trip has ever been suggested by medical professionals. (Aspirin affects the blood differently than warfarin.)
I wouldn't worry too much, however. Hope you're planning a fun destination and will report back here on your return.