Systems, devices, and methods for pacing a heart of a patient are disclosed. An illustrative method may include determining a motion level of the patient using a motion sensor of an implantable medical device secured relative to a patient's heart, and setting a pacing rate based at least in part on the patient's motion level. The patient's motion level may be determined by, for example, comparing the motion level sensed by the motion sensor during a current heart beat to a motion level associated with one or more previous heart beats. Noise may occur in the motion level measurements during those heart beats that transition between an intrinsically initiated heart beat and pace initiated heart beat. Various techniques may be applied to the motion level measurements to help reduce the effect of such noise.
