Modern computer power allows development of models of the heart that may be helpful for the understanding of arrhythmia mechanisms if, based on realistic physiological parameters, such models can display phenomena difficult to study in nature. Therefore, a two-dimensional model of the cardiac tissue has been implemented, where the modeling of each cell is based on membrane ionic channels (Beeler-Reuter and Luo-Rudy models). In addition, an ECG was computed based on the ionic currents simulated. This model allows us to observe the propagation of the action potentials Vm across the cardiac tissue, the evolution of Vm for any of the cardiac cells, and the underlying ionic currents. The computation of the ECG makes it possible to relate this information with an often-used diagnostic tool. Simulations of normal and pathological phenomena such as functional and anatomic reentry have been performed. Our simulation results show that the applied computer model based on ionic currents seems accurate and realistic when compared with biological models and offers a new approach to study the origin, prevention, and termination of arrhythmias.