Summary: This paper introduces an approach for modeling the calcium electrodynamics in cardiac fiber taking into account the electrostatic capacitance, non-reactive (ohmic) resistance, negative reactive resistance and small inductivity of the reticulum membrane. Proposing the simplest analytic form of competition between \(\text{Ca}^{2+}\) ions and ATP molecules at the calcium pump, the nonlinear differential equation of Van der Pol type for the calcium concentration in the myoplasma is derived. Using the capacitance formula the same equation is transformed for describing the action potential behavior in the muscle contraction process. The phase and bifurcation analyses of this model are presented. Physiologic interpretation of the qualitative results, oriented to further development of the problem, is made.