An intracardiac ventricular pacemaker is configured to detect an atrial mechanical event from a motion sensor signal received by an atrial event detector circuit of the pacemaker. The motion sensor signal is responsive the motion of blood flowing in the ventricle. A pacing pulse is scheduled at an expiration of a pacing interval set by a pace timing circuit in response to detecting the atrial mechanical event. An atrial-synchronized ventricular pacing pulse is delivered upon expiration of the pacing interval.
