The electrocardiogram (ECG), is a recording of the heart’s electrical activity. This electrogram is a graph of voltage versus time of the electrical activity of the heart using electrodes placed on the skin. The electrodes detect the small changes that are caused by cardiac muscle depolarization and repolarization during each heart cycle (heartbeat). An abnormal ECG can be seen in numerous cardiac conditions, such as irregular heart rhythms, inadequate coronary artery blood flow, and electrolyte disturbances.