The work is devoted to the construction of an asymptotic observer for a pacemaker model based on the Van der Pol equation. The cardiac system can be represented as a combination of three oscillatory circuits: the sino-atrial node (pacemaker), the atrio-ventricular node, and the ventricular conducting system, models of which can be constructed using the Van der Pol equation. In practice, only the values of the potentials of the nodes are measurable, while the rates of their changes are not directly measured. The work of the asymptotic observer with linear dynamics of error constructed in the work is illustrated by the mathematical modeling.