A mechanical model of cardiac muscle taking account of excitation-contraction coupling

A three-dimensional transversely isotropic constitutive model of cardiac muscle is proposed. Stress in the cardiac muscle is first divided into the sum of passive and active parts. The passive part is represented by a strain energy, density function of the exponential type, while the active part is formulated by introducing internal variables describing the activities and the sarcomere length. The evolution equations of the internal variables are established by taking account of excitation-contraction coupling. Comparison of the simulation results with those of experiments in the literature shows that the present model can describe qualitatively the mechanical properties of cardiac muscle.