The interference voltage at the terminals of a unipolar-type implantable cardiac pacemaker induced by a near-field intra-body communication device was investigated by numerical calculations. Operating frequency was assumed 5 MHz. The dependency of induced voltage on the electrical constants of a realistic human model was examined. The results showed that the induced voltage was inversely proportional to the absolute value of the complex relative permittivity. The induced voltage was much smaller than the immunity requirement on interference voltage for active medical implants when the applied input voltage to the communication device was within the practical use condition.