Pacemakers are not a big deal, for the most part. The typical pacemaker that only cuts in when the HR drops to a set value, does not represent any additional risk to a person. They can go wide open and need not worry. A de-fib pacemaker may present some small amount of risk, although one of the fastest cyclists in our area has one and it doesn't hold him back at all. I guess any additional concerns or risks would be tied more to any heart conditions or anomalies, not so much the pacemaker.