Baseline BiV pacing is delivered and a corresponding baseline BiV efficacy score is determined. Intrinsic AV conduction is allowed and an intrinsic AV conduction interval is determined. BiV fusion pacing is delivered and a corresponding efficacy score is determined, for each of a plurality of different paced AV delays, each determined based on the intrinsic AV conduction interval and a different negative hysteresis delta. The baseline BiV pacing is selected for delivery during a period of time if the baseline BiV efficacy score is better than all of the efficacy scores. BiV fusion pacing is selected for delivery during the period of time, using one of the plurality of different paced AV delays for which a corresponding efficacy score was determined, if the efficacy score corresponding to at least one of the plurality of different paced AV delays is better than the baseline BiV efficacy score.