Abstract: A cardiac pacemaker and related pacing method. The cardiac pacemaker includes atrial and ventricular sense amplifiers for generating atrial and ventricular sense signals. An activity control circuit measures the activity level and initiates an activity interval. A control circuit responds to the atrial sense signals, the ventricular sense signals, and the activity control circuit, for controlling the atrial and ventricular stimuli generation, by matching the activity interval with the depolarization of the atrial tissue, in order to differentiate true exercise induced sinus tachycardia from atrial arrhythmias and retrograde atrial events, and to permit a selective ventricular rate control. The control circuit initiates a 2 to 1 ventricular to atrial response when the activity interval is greater than a VV interval, which is the sum of the interval between the last sensed or paced ventricular event and the atrial intrinsic depolarization (VA.sub.