The invention relates to cardiac rhythm management systems, and more particularly, to rate adaptive cardiac pacing systems and methods. In an embodiment, the invention includes a method for providing rate-adaptive cardiac pacing therapy from an implantable medical device, the method including sensing a pulmonary function of a patient； determining a rate of change in the pulmonary function； sensing a cardiac function of the patient； determining a rate of change in the cardiac function； and calculating a target pacing rate based on an existing pacing rate, the rate of change in the pulmonary function, and the rate of change in the cardiac function. In an embodiment, the invention includes a method of controlling a cardiac rhythm management device in response to exertion of a patient, the method including sensing the patient's pulmonary function at a first time t1 and at a second time t2； calculating a rate of change of the pulmonary function between time t1 and time t2； sensing the patient's cardiac function at time t3 and t4； calculating a rate of change of the cardiac function between time t3 and time t4； and setting a desired pacing rate. Embodiments of the invention also include cardiac rhythm management devices.
