A dual chamber pacemaker is provided having capability for adjusting the AV escape interval so as to optimize the timing of delivered ventricular pace pulses for therapy of patients with cardiomyopathy. The pacemaker system continually monitors to determine when a delivered pace pulse results in a fusion beat, and periodically adjusts the AV escape interval in accordance with the percentage or rate of incidence of such fusion beats. In one specific embodiment, the pacing system determines the percentage of delivered ventricular pace pulses which are followed by fusion beats over a predetermined number of intervals, and decrements AV escape interval when such percentage is not below a predetermined minimum. The pacing system also periodically increments AV escape interval when the rate of fusion beats is acceptable, thereby providing a closed loop system for maintaining the AV interval at an optimally long value consistent with maximizing full capture by delivered ventricular pace pulses. In another embodiment, the V-V escape interval of a non-tracking mode pacemaker is controlled to optimize pre-excitation of the ventricle.