15 different models of implanted demand pacemakers (61% Cordis models) in 156 patients were scrutinized owing to an announcement that had identified 3 faulty Cordis series and, as a consequence, had provoked considerable uncertainty among all pacemaker patients in the community. Malfunctions of the sensing, and reed switch mechanisms as well as changes in pacers' refractory periods were excluded by the electrical chest wall stimulation (ECWS), magnet waving (MW) or a combination of both. That those models suspected of malfunction show merely a drop in rate was verified. Established patterns of early rate drop guided the exchange for new units: no abrupt or complete rate drop occurred and no patient was lost. The application of indirect overdrive revealed that the blocking capacity for rapid rates was in Omni-Ectocor units less reliable than in Ectocor units. The characteristic reactions to MW and ECWS of the 15 demand pacemaker models were determined. Because both methods proved to be as easy to apply as they were beneficial for the follow-up, also in the uncommon situation created by the Cordis announcement, the application of both of these methods on a routine basis in pacemaker clinics is advocated.