Our research group has conducted many computer simulation studies over the past years, in order to comprehensively understand the electrophysiological phenomena in the heart. By developing high performance computing techniques and visualization technology and by integrating the multilevel knowledge obtained through basic studies from the ion channel level to the organ morphology level, we have simulated the electrical activities of the heart. Actually, incorporating many experimental multilevel data in heart models and executing simulations are difficult tasks. It is necessary to idealize a model as much as possible for realization of an effective and comprehensible simulation. In this article, we report two studies in which one or two thousand units of FSK model designed from the electrophysiological characteristics of ion channels in myocardial cell were linked and large-scale simulations of electrical activities were conducted on a super-computer. The first study was a filament analysis of rotary pivots of scroll wave reentrant arrhythmic activities in a three-dimensional ventricular wall slab model. The results suggested a defensive function against arrhythmia in the heart and a proarrhythmic function caused by degeneration of the defensive function. The second study indicated the dynamics of electrical activities caused by delayed conduction region in the right ventricular outflow tract based on hypothetical Brugada syndrome. Although the three-dimensional ventricular shape model does not sufficiently incorporate detailed physiological properties of the heart, we speculate that this study has generated some inspiring data.