A device for detecting tachycardiac rhythm disturbances, has a measuring unit for picking up and reproducing a measurement signal dependent on intracardial impedance at its output and an evaluation unit connected at the input to the measuring unit. The evaluation unit is adapted to output both a first signal which corresponds to the difference of a maximum and a minimum measurement signal within at least one predeterminable period of time and also a second signal which is dependent on the integral of the measurement signal over at least one predeterminable period of time.