Can I Measure HRV if I Use a Pacemaker?

This is a great question that arises from time to time; as each individual is different, there is no single answer.

If the pacemaker is actively pacing, then it will skew the HRV reading and likely not be useful. 

If the pacemaker is not actively pacing when you take your HRV readings, and you take many readings over time, then the relative changes in HRV over time could still be useful to see.