Training effect HR vs power

I’m interested to know if a rising heart rate at steady power will take me out of zone when I’m doing foundation work. I’ve just done over an hour at 120 watts and I’ve varied cadence and position on the bars at 5 minute intervals. HR rose from 120s to 140s over the session especially during high cadence sectors.

I suppose it depends on your definition.
Most workouts I’ve seen defined zone by power.
The older ones were HR based.
I’ve not seen a system that employed both.
If you held 120 watts, then you stayed in the same power zone but obviously your HR zone increased.
Good Question and I hope some coaches respond.