Abstract: A cardiac pacemaker includes means for conforming the stimulation frequency to the bodily stressing conditions of the wearer of the pacemaker in using a blood parameter as measuring value for the influencing of the frequency of stimulation. A measuring probe is implanted in the heart of the wearer of the pacemaker for measuring the oxygen saturation of the blood. The measuring value thereby resulting serves as measuring parameter for the influencing of the frequency of stimulation.