A pacemaker is configured to deliver pacing pulses that lead pacing pulses delivered by another medical device. The pacemaker may detect pacing pulses delivered by the other medical device by a pulse detector circuit of the pacemaker, produce a pulse detect signal in response to each one of the detected pacing pulses, determine a pulse detect interval between two pulse detect signals consecutively produced by the pulse detector circuit, set a pacing escape interval based on the pulse detect interval less a pre-interval, and deliver a pacing pulse upon expiration of the pacing escape interval.