I came home from Heathrow just a few weeks ago - have had a pacemaker for a couple years. My experience is much like some of the other posters above. When you get close to the WTMD, just pat your chest, say pacemaker, and they bring you into a patdown area rather than making you go through the WTMD. No problem at all at Heathrow, and I've had so many patdowns now (probably 100+ in the past 2 years of flying) that I almost don't notice it any more. The only one that ever really got me agitated was when one odd TSA person wanted to do the patdown with the hand-held metal detector turned off, so that she wouldn't have to use her hands. I refused - how could I tell whether she would turn it on mid-screening? she got another screener. The only other odd one was this TSA person who had an aversion to touching velvet, even through gloves and told me she couldn't do my patdown! She finally realized it was OK when I told her my pants were suede, not velvet. Seems like not being able to bring yourself to do a patdown should disqualify you from being a TSA agent in a patdown area. In any event, pacemakers are pretty routine for the TSA - though now they may try to make you go through the new scanners instead of having a patdown. I still prefer the patdown to a virtual strip search. And like others, I always pull my pacemaker ID card out of my wallet and have it in hand along with my photo ID and boarding pass. I will flash it if I get any confused looks from the TSA, but I've never been required to present it for any sort of thorough check.