A cardiac pacemaker model is described based on a close approximation of the properties of cardiac pacemaker cells. It is a minimum-parameter model which has a simple relaxation oscillator circuit as its main element. The pacemaker model is analyzed in detail in order to show that its behaviour is similar to that of cardiac pacemaker cells. The main feature of the model is the possibility of controlling the time course of phase 4 depolarization, the threshold level and the maximum level of repolarization. Emphasis is placed on phenomena of acceleration and deceleration of the pacemaker model by pulsatile stimulation, and on synchronization and frequency entrainment. Finally it is noted that this particular pacemaker model is very useful for the study of interactions between cardiac pacemakers and the description of the mechanism of arrhythmias.