A medical device performs a method for controlling a cardiac pacing therapy. The device determines an inter-atrial conduction time (IACT) and compares the IACT to a threshold. A controller included in the device sets a pacing interval for controlling delivery of pacing pulses to a ventricle to a first ventricular pacing interval that expires after the IACT in response to the IACT being less than the threshold and sets the pacing interval to a second ventricular pacing interval that expires before the IACT in response to the IACT being greater than the threshold.