Arrhythmia refers to any change from the normal sequence of electrical impulses, causing abnormal heart rhythms. With the help of well-known Beeler - Reuter mathematical model of a cardiac cell, we demonstrate that some of the clinically observed manifestations of arrhythmia property can be simulated. In our simulation study a 60×60 network of cells is considered. The cells are coupled through resistive element. These resistive elements are similar to gap junction in real cardiac tissue. An input stimulus is presented in addition to ionic current to generate action potential continuously, since ventricle cells are not oscillatory. The input stimulus is presented in a group of cells at the left most corner of the grid of cells at specific instant of time. The selection of duration and amplitude of input stimulus plays a vital role. The presentation of input stimulus makes a regular cardiac rhythm traveling from left top most corner to right bottom corner in the grid. External signals are applied in the grid of cells to disturb a regular rhythmic pattern to simulate arrhythmia condition and leads to generation of spiral waves. This situation is clinically identified as re-entrant arrhythmia. The external signals are Gaussian in nature having a frequency same as that frequency of action potential in that region. It is observed that the location of presentation of external signal leads to different kinds of abnormalities. This above study was performed using nominal initial values for all the variables. It is further observed that increase in sodium ion conductance from nominal value does not disturb the regular rhythmic pattern even with the application of external Gaussian signal. This shows an initial step in identifying the role of sodium ions in arrhythmias. Also we have studied the similar simulation study with 90×90 grids of cells.