Electrical Play above the waist (mainly in the torso, but not exclusively) can interfere with the body's natural electrical impulses to the heart. All electrical players must be aware of this risk. Electrical play should be done with EXTREME care, or not done at all, to people with heart trouble and especially pacemakers!
A reader wrote in with the following clarification:
"Actually, no actual 'electrical impulses' flow from the body to the heart that have anything to do with maintaining a heartbeat. The heart beats on its own (even for many hours if removed and kept in Ringers') and that heartbeat rhythm originates spontaneously from the pacemaker (sinoatrial node) which is part of the heart itself.
The danger from electrical currents passing through the thoracic region is that you will interrupt the communication between this natural pacemaker, the parts of the heart that communicate the signals around the heart, and the heart itself (because actually all of these will "beat" on their own, unfortunately at their own rhythms) causing the heart to beat and contract randomly in all odd directions in different parts (fibrillation), meaning it really can't pump anything at all (and that's not a true "heart attack" either).
As a point of interest, this is the principle defribrillators work on: contrary to popular opinion, they can't do a thing to re-start your heart. What they actually do stop it all at once, in the hope that your natural pacemaker will reassert control and get a regular heartbeat and contractions going again.
Not to be picky, but I wanted you to know so that if you feel like it you can change it to get the details correct (that it'll screw up the heart itself, not any kind of heart-brain connection) so that the rest of your highly valuable BMErisks won't be disregarded by someone who picks out this detail as incorrect and thinks the rest may be as well."