Cardiac arrhythmias are mainly due to failure in the coordination among contraction of cardiac muscle. Among several types of arrhythmias, we focused on ventricular reentrant arrhythmia because it is more dangerous arrhythmia. With the help of detailed biophysical model of human ventricular cell, the role of sodium ion concentration and calcium currents on single and one-dimensional array of cells in establishing arrhythmias are studied. Two simulation studies have been made. First study showed the effect of variation in sodium ion concentration and calcium current on single cell behavior. In the next study, onedimensional array of cell is coupled via gap junction conductance and it is observed that there is change in propagation of action potentials (i.e. action potential duration, notch in AP and flow of ionic currents among cells) due to the variations in ion concentration as well as calcium currents are well studied. The effect of drugs and some external influence (tension, stress in cardiac system) in real environment causes abnormalities in cardiac electrical activity due to the changes in ionic concentration. This motivated to study how variation in ionic concentration leads to arrhythmia by simulation. © 2006 Research Publishing Services.