Final answer:
A magnet should be placed over a pacemaker if the patient is pacemaker dependent (persistent bradycardia, 3rd degree AV block) in order to temporarily deactivate or inhibit the pacemaker's function.
Step-by-step explanation:
A magnet should be placed over a pacemaker if the patient is pacemaker dependent (persistent bradycardia, 3rd degree AV block) in order to temporarily deactivate or inhibit the pacemaker's function. This is done in emergency situations where the pacemaker is malfunctioning or causing harm to the patient. By placing a magnet over the pacemaker, the device's sensors are disabled and it will no longer deliver electrical impulses to the heart, allowing the patient's natural heartbeat to take over.