Computer simulation using Luo-Rudy I1 model of ventricular myocyte showed that intracellular calcium dynamics become irregular in case of high rate stimulation. This causes the transition from stationary to nonstationary spiral wave and its breakup in 2D model of cardiac tissue. Obtained results suggest how ventricular fibrillation may occur due to the abnormalities of intracellular calcium dynamics. The short review of existing cardiac cell models with calcium dynamics is presented.