A challenge for pacemaker therapists is whether a patient working in an environment with the potential for electromagnetic interference (EMI) can return to their work after a pacemaker has been implanted. Common practice has been to prohibit pacemaker patients from using electric welding machines. Twelve work environments and a new method for monitoring the pacemaker rhythm in the presence of EMI were tested. The new method uses a special memory called the event record found in several Siemens Pacesetter pacemaker models. Surface ECGs with a marking system, intracardiac electrograms, and a digital monitor were used to verify the results with event records. The results from several sources of EMI are reported. Twenty-one in vivo and in vitro tests were performed in the work environments of 12 patients. Event records were useful and accurate both in vivo and in vitro. Electric are welding machines up to 225 A did not affect these pacemakers. Arc welding machines using 1,000 A or more inhibited the in vitro test system within 1 or 2 meters of the weld or power generator. Electric welding machines with high frequency voltage superimposed on the welding current affected the pacemaker when it was within 2 meters of the power unit and 1 meter of the weld. Very large industrial degaussing coils affected pacemakers within 2 meters. The test method using event records was found to be an effective addition to monitoring the pacemaker. These results are specific for the pacemaker models tested. Such testing allows the physician to make a knowledgeable decision regarding return to work for the pacemaker patient in a high EMI environment.