I have a pacemaker and have never had any problems receiving reflexology.
When newly inserted you should probably treat the reflex area gently and have a soothing intent, the same for any post op area.
After that treat in the usual way you would for heart conditions. ie light pressure with a healing intent, picturing a healthy heart.
The actual area should not be vigorously massaged if having a body massage, as they are rate responsive these days and might iincrease the beats, not very relaxing!
Jan