I've been going through security with a Pacemaker for 15 years, and it has Never been a problem. It has never set off the metal detector.
Most, if not all, pacemakers are now properly shielded so that the detectors do not effect them, and they do not show up by the detectors. They will show in x-rays, of course.

When I first got my pacemaker I was very reluctant to go through so I asked for a pat down. I no longer do that as I fear that will end up to be much more than a little patdown with the "new" procedures. I just walk through & go on my merry way.