An electrical pulse generator system such as a cardiac pacemaker or defibrillator system includes an impedance measuring device which measures the impedance across pacemaker leads, a display device, and a controller which controls the display device to display at least the measured impedance upon each stimulation pulse, or an image showing the relationship between a first applied electrical signal, measured impedance, and a resulting electrical signal which varies according to Ohm's Law. The system may include a short circuit detector and a pulse amplitude control module which switches between normal mode and safe mode operation based on short circuit detection, with different maximum stimulation pulse amplitudes in the normal and safe modes.