Wherever there are electromagnetic fields (EMFs), there are potential problems for people with pacemakers. Magnetic resonance imaging (MRI) scans can cause the devices to malfunction. In one report, several people in the US with pacemakers died after having an MRI (BMJ, 1991; 303: 205).

Any number of more commonplace electrical devices can also cause problems. Overhead power lines may cause irregular unit function (PACE, 1983; 6: 1282-92). The EMF generated by anti-shoplifting devices can also cause palpitations, nausea, dizziness and breathing difficulties each time the cardiac patient passes through them. Doctors therefore warn people with pacemakers to either avoid these systems or endeavour to pass through them as quickly as possible (N Engl J Med, 1998; 339: 1371-4).

Mobile phones may also cause problems. Studies have shown that some cellular phones, when placed close to implanted pacemakers, can interfere with the operation of the pacemaker (N Engl J Med, 1997; 336: 1473-9).

More recent studies show that interference seems to occur with digital cellular phones when they are closer than three inches from the pacemaker. The interference is generally temporary and disappears when the phone is switched off or moved away from the pacemaker. However, users should be aware of the possibility of interference even when the phone is in stand-by mode.