The invention concerns implantable cardiac stimulation devices in general which have at least one stimulation pulse generator (A-STIM; RV-STIM; LV-STIM) to selectively generate a stimulation pulse for delivery to one of at least two different chambers of a heart, said chambers include right and left atria and right and left ventricles, at least one impedance measuring stage (I, U, IMP) being connected to electrodes or connectors for such electrodes to measure an intracardiac impedance when in use, a control unit (CTRL) connected to the stimulation pulse generator and to the impedance measuring unit and being adapted to process a minimum impedance value for a heart cycle to trigger stimulation pulses for two different chambers of the heart with an adjustable time delay (VVD; AVD) and to adjust said time delay depending upon the measured intracardiac impedance minimum value. According to the invention the control unit is adapted to adjust the time delay such that the minimum value of the intracardiac impedance during one heart cycle is minimized or such that the AVD delay is equal to the time interval between an atrial event and the point of time when the minimum impedance value occurs after said atrial contraction.