A:Answer I can't give you medical advice, but I have a pacemaker and the Apple Watch works just fine with it. I have had no problems and I am not aware of any reason the Apple watch would cause any problems with a pacemaker or ICD.
I also use a Polar chest strap and Polar watch to monitor my heart rate while working out in addition to wearing the Series 4 Apple Watch all of the time including during exercise.
The watches are not medical devices, but work well for me to get additional health information.