A system comprising a cardiac pacemaker and an Implantable Cardioverter Defibrillator, ICD, that is configured to provide defibrillation therapy, the cardiac pacemaker comprising: one or more sensors for sensing one or more physiological parameters of a patient; two or more pacing electrodes for delivering pacing pulses to the heart of the patient; electronics (102, 104, 104, 106, 108, 110, 112) operatively coupled to the one or more sensors and the two or more pacing electrodes, the electronics (102, 104, 104, 106, 108, 110, 112) is configured to: determine a heart rate of the patient based at least in part on the one or more physiological parameters sensed by the one or more sensors; pace the heart of the patient via the two or more pacing electrodes in a manner that attempts to keep the heart rate of the patient from falling below a demand heart rate threshold, wherein: the pacing pulses are delivered at a capture pacing energy level; characterized in that when the heart rate rises above an upper heart rate threshold, the cardiac pacemaker autonomously sets the pacing pulses to an enhanced energy level above the capture pacing energy level regardless of whether defibrillation therapy is delivered or not, and without first having to detect a high energy shock pulse or receive a communication from another medical device notifying the cardiac pacemaker that a shock will be delivered, wherein the cardiac pacemaker sets the energy level of the pacing pulses to an enhanced energy level for a temporary period of time, and then returns the energy level back to the capture pacing energy level. one or more sensors for sensing one or more physiological parameters of a patient; two or more pacing electrodes for delivering pacing pulses to the heart of the patient; electronics (102, 104, 104, 106, 108, 110, 112) operatively coupled to the one or more sensors and the two or more pacing electrodes, the electronics (102, 104, 104, 106, 108, 110, 112) is configured to: determine a heart rate of the patient based at least in part on the one or more physiological parameters sensed by the one or more sensors; pace the heart of the patient via the two or more pacing electrodes in a manner that attempts to keep the heart rate of the patient from falling below a demand heart rate threshold, wherein: the pacing pulses are delivered at a capture pacing energy level; characterized in that when the heart rate rises above an upper heart rate threshold, the cardiac pacemaker autonomously sets the pacing pulses to an enhanced energy level above the capture pacing energy level regardless of whether defibrillation therapy is delivered or not, and without first having to detect a high energy shock pulse or receive a communication from another medical device notifying the cardiac pacemaker that a shock will be delivered, wherein the cardiac pacemaker sets the energy level of the pacing pulses to an enhanced energy level for a temporary period of time, and then returns the energy level back to the capture pacing energy level. determine a heart rate of the patient based at least in part on the one or more physiological parameters sensed by the one or more sensors; pace the heart of the patient via the two or more pacing electrodes in a manner that attempts to keep the heart rate of the patient from falling below a demand heart rate threshold, wherein: the pacing pulses are delivered at a capture pacing energy level; characterized in that when the heart rate rises above an upper heart rate threshold, the cardiac pacemaker autonomously sets the pacing pulses to an enhanced energy level above the capture pacing energy level regardless of whether defibrillation therapy is delivered or not, and without first having to detect a high energy shock pulse or receive a communication from another medical device notifying the cardiac pacemaker that a shock will be delivered, wherein the cardiac pacemaker sets the energy level of the pacing pulses to an enhanced energy level for a temporary period of time, and then returns the energy level back to the capture pacing energy level. the pacing pulses are delivered at a capture pacing energy level; characterized in that when the heart rate rises above an upper heart rate threshold, the cardiac pacemaker autonomously sets the pacing pulses to an enhanced energy level above the capture pacing energy level regardless of whether defibrillation therapy is delivered or not, and without first having to detect a high energy shock pulse or receive a communication from another medical device notifying the cardiac pacemaker that a shock will be delivered, wherein the cardiac pacemaker sets the energy level of the pacing pulses to an enhanced energy level for a temporary period of time, and then returns the energy level back to the capture pacing energy level.