Systems and methods for rate-adaptive pacing are disclosed. In one illustrative embodiment, a medical device for delivering electrical stimulation to a heart may include a housing configured to be implanted on the heart or within a chamber of the heart, one or more electrodes connected to the housing, and a controller disposed within the housing. The controller may be configured to sense a first signal and determine a respiration rate based at least in part on the sensed first signal. In at least some embodiments, the controller may be further configured to adjust a rate of delivery of electrical stimulation by the medical device based at least in part on the determined respiration rate.
