There is disclosed a dual chamber pacer which offers several advantages over prior art devices. Although the pacer requires for its operation AV delay and VA delay parameter values, most physicians characterize dual chamber pacers in terms of AV delay and ventricular pacing rate. The pacer of the invention can be programmed under external control by the physician setting values for the parameters with which he is most familiar. A subtractor in the pacer forms the difference between the reciprocal of the ventricular pacing rate and the AV delay to derive the value of the VA delay. The pacer is also characterized by active recharge of the atrial output capacitor so that a very short ventricular refractory period following atrial pacing may be provided. A single maximum rate timer prevents the generation of excessively fast ventricular stimuli, whether due to the ventricular or atrial sub-systems, or even if atrial contractions are being sensed at too rapid a rate.