Filter pass-band settings have impact not only on ECG output amplitude, but also on output signal wave-form of some types of digital electrocardiograph. Lower cut-off frequency is decided by Wander filter setting for some types of digital electrocardiograph, and higher cut-off frequency is decided by muscle filter when muscle filter functionality is "on". We research into various filter settings' impact on the output of digital electrocardiograph and have discussions on the malfunctions found in digital electrocardiograph measurement.