In order to investigate the characteristics and underlying mechanisms of Ca²⁺ wave propagation, we developed a 3D simulator of cardiac myocytes, in which the sarcolemma, myofibril and z-line structure with Ca²⁺ release sites were modeled as separate structures using the finite element method. Similarly to previous studies, we assumed that Ca²⁺ diffusion from one release site to another and calcium-induced calcium release were the basic mechanisms, but use of the finite element method enabled us to simulate not only the wave propagation in 3D space but also the active shortening of the myocytes. Therefore, in addition to the dependence of the Ca²⁺ wave propagation velocity on the sarcoplasmic reticulum Ca²⁺ content and affinity of troponin C (TnC) for Ca²⁺ , we were able to evaluate the influence of active shortening on the propagation velocity. Furthermore, if the initial Ca²⁺ release took place in the proximity of the nucleus, spiral Ca²⁺ waves evolved and spread in a complex manner, suggesting that this phenomenon has the potential for arrhythmogenicity. The present 3D simulator with its ability to study the interaction between Ca²⁺ waves and contraction will serve as a useful tool for studying the mechanism of this complex phenomenon.