Abstract: A cardiotachometer includes features which reliably filter out interfering background signals and provide for relatively low power consumption. A differential amplifier is connected to a three electrode input so as to effectively reduce common mode errors. The output of the differential amplifier is connected to an automatic polarity selecting circuit and an automatic gain control amplifier so as to make the unit as independent as possible from user adjustment. The device includes an eight bear counter for producing a single output pulse for every eight input pulses. The output of the eight beat counter is connected to a dual slope analog-to-digital converter for developing a display which is directly related to the average heart rate over a eight beat period and inversely related to the voltage applied to the circuit. A low power liquid crystal display is connected to the output of the dual slope circuit.