Just to agree with Steve on the Pacemaker point - they are a piece of cake if needed. My reason for getting one was different - I have complete heart block because of surgical complication, or in other words my heart doesn't beat on its own at all because they damaged the natural electrics of the heart during surgery. Even the warnings about not going through airport scanners seem unnecessary - I told security staff the first couple of times, and went around for a manual pat-down etc, but not bothered since then.
Having said that, I think I am right in saying that pacemakers generally act as a 'safety net', ensuring that your heart beats as much as it should, but don't help with slowing a heartbeat down (like tachycardia) unless they deliberately cut the heart's electrics (the AV node) so that the pacemaker takes full control. I would look into this more if this applies to you.