A single chamber cardiac pacing system configured to be wholly on or in a patient's heart, the system including: implantable electrodes (111, 112); a pulse generator coupled to the electrodes; one or more rate response sensors: means for establishing a baseline rate for pacing stimulation according to input from the one or more rate response sensors; means for establishing an offset rate for pacing stimulation, the offset rate being lower than the baseline rate and generally tracking therewith such that a difference between the baseline rate and the offset rate remains substantially constant over time; means for sensing for intrinsic cardiac events by means of the implanted electrodes; means for applying a pacing stimulation pulse by means of the implanted electrodes, responsive to an intrinsic event is not being sensed within a time interval necessary to at least maintain the offset rate, the applied pacing stimulation pulse creating a paced event to maintain the offset rate; characterised by means for switching from the offset rate to the baseline rate and triggering pacing at the baseline rate over a predetermined period of time, responsive to x of y successive cardiac events being paced events, x being greater than one and y being greater than or equal to x; and wherein the offset rate is established according to a predetermined decrement of one of: the baseline rate; and a greater of the baseline rate and an intrinsic heart rate, the intrinsic heart rate determined according to prior sensed intrinsic events. implantable electrodes (111, 112); a pulse generator coupled to the electrodes; one or more rate response sensors: means for establishing a baseline rate for pacing stimulation according to input from the one or more rate response sensors; means for establishing an offset rate for pacing stimulation, the offset rate being lower than the baseline rate and generally tracking therewith such that a difference between the baseline rate and the offset rate remains substantially constant over time; means for sensing for intrinsic cardiac events by means of the implanted electrodes; means for applying a pacing stimulation pulse by means of the implanted electrodes, responsive to an intrinsic event is not being sensed within a time interval necessary to at least maintain the offset rate, the applied pacing stimulation pulse creating a paced event to maintain the offset rate; characterised by means for switching from the offset rate to the baseline rate and triggering pacing at the baseline rate over a predetermined period of time, responsive to x of y successive cardiac events being paced events, x being greater than one and y being greater than or equal to x; and wherein the offset rate is established according to a predetermined decrement of one of: the baseline rate; and a greater of the baseline rate and an intrinsic heart rate, the intrinsic heart rate determined according to prior sensed intrinsic events. means for establishing a baseline rate for pacing stimulation according to input from the one or more rate response sensors; means for establishing an offset rate for pacing stimulation, the offset rate being lower than the baseline rate and generally tracking therewith such that a difference between the baseline rate and the offset rate remains substantially constant over time; means for sensing for intrinsic cardiac events by means of the implanted electrodes; means for applying a pacing stimulation pulse by means of the implanted electrodes, responsive to an intrinsic event is not being sensed within a time interval necessary to at least maintain the offset rate, the applied pacing stimulation pulse creating a paced event to maintain the offset rate; characterised by means for switching from the offset rate to the baseline rate and triggering pacing at the baseline rate over a predetermined period of time, responsive to x of y successive cardiac events being paced events, x being greater than one and y being greater than or equal to x; and wherein the offset rate is established according to a predetermined decrement of one of: the baseline rate; and a greater of the baseline rate and an intrinsic heart rate, the intrinsic heart rate determined according to prior sensed intrinsic events.