A heart stimulator having an electric input that is connectable to a plurality of electrodes is disclosed and includes a stimulation control unit, one or more stimulation units, an impedance determination unit and an impedance evaluation unit. The stimulation units generate stimulation pulses and deliver a stimulation pulse when triggered by the stimulation control unit. The stimulation control unit is operatively connected to one or more stimulation units to control pacing parameters such as pacing site and/or the timing of stimulation pulses to be delivered by the one or more stimulation units. The impedance determination unit determines impedance values reflecting intracardiac impedance, and the impedance evaluation unit evaluates the impedance values and provides an evaluated impedance signal to the stimulation control unit. The impedance determination unit determines a plurality of impedance values between different pairs of electrodes that are connected to the electric input during operation of the heart stimulator.
