A cardiac pacemaker with a rate stabilization pacing mode. The pacemaker varies the increment following a cycle ending in a sensed depolarization as a function of the underlying heart rate and may additionally vary the increment as a function of the prematurity of the most recently sensed depolarization relative to the preceding depolarization. A greater increment is generally provided if the underlying cycle length is greater, while the increment may be lessened following relatively more premature depolarizations. Prematurity may be determined by comparing the cycle (CLnew) ending in the most recently sensed depolarization with the previous cycle length (CLold), for example by calculating CLnew/CLold or CLold-CLnew. The mechanism for determining the duration of the increment provides for a more rapid return to a lower underlying heart rate, while still avoiding the short- long interval pattern sometimes associated with the onset of tachycardia.
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