The dual chamber system and method of operation contains an automatic test for determining an optimum AV interval at a test frequency such as LRL. In a preferred embodiment the test is carried out at nighttime, wherein the implanted pacer is set to asynchronous operation at LRL, and AV interval is sequenced through a range from a predetermined AV.sub.min to a predetermined AV.sub.max. The QT interval corresponding to each respective AV interval is determined and stored; the QT data is analyzed to determine the maximum QT interval; and the optimum AV is determined at that which corresponds to the maximum QT. The optimum AV interval thus found is incorporated into the pacer memory for use in timing out AV interval. The optimum AV data may be utilized for determining AV=f.sub.s (rate) for calculating AV interval following each AS, as well as AV=f.sub.p (rate) for calculating AV interval following an atrial pace. Alternately, a test can be performed to determine whether an incremental adjustment of AV delay is indicated. In accordance with the invention, a DDDR pacer with automatic AV delay control can be achieved, without need for an extra sensor.