A rate-adaptive cardiac pacemaker has a detection unit 1, an event-determining unit 2, a stimulation control unit 3 and a stimulation unit 11, wherein the event-determining unit 2 is connected to the detection unit 1 and the stimulation control unit 3, and the stimulation unit 11 is connected to the stimulation control unit 3. The detection unit 1 detects ECG signals of a heart 100, and the event-determining unit 2, on the basis of the ECG signals detected by the detection unit 1 and signals emitted by the stimulation control unit 3, determines whether a detected event represents a spontaneous or a stimulated event (A.sub.p, A.sub.s; AES, V.sub.p, V.sub.s, VES). The stimulation control unit 3 ascertains a stimulation rate based upon a base rate and a physiological demand and varies the base rate based upon the event-determining unit 2 in a first mode, when atrial events occur in such a way that in the case of a spontaneous atrial event a spontaneous interval is prolonged by a first change value and that in the case of a stimulated atrial event a base interval is prolonged by a second change value, whereby in both cases the base rate is lowered, and in a second mode, when ventricular events occur, the stimulation control unit 3 varies the base rate in such a way that in the case of a spontaneous ventricular event the base rate is raised and in the case of a stimulated ventricular event the base rate is lowered. The stimulation unit stimulates the heart in accordance with the signals received from the stimulation control unit 3.