Low frequency electric and magnetic fields may interfere with implanted cardiac pacemakers causing a life-threatening malfunction of the device. In order to assess the safety of workers in the vicinity of industrial electrical devices the interference voltage at the input port of a pacemaker is an important measure. In order to investigate the coupling of fields emanating from electrical devices a numerical method for the calculation of interference voltages is presented and applied to the investigation of homogeneous electric and magnetic fields in the frequency range from 50 Hz to 1 MHz. Implantation of the pacemaker in the right pectoral, left pectoral and abdominal area using a realistic model of the human body as well as different grounding conditions are considered. The numerical method is successfully validated by measurements and shows good agreement with results in the literature.