Electrocardiography
 is the process of producing an electrocardiogram (ECG or EKG[a]), a recording
 of the heart's electrical activity.It is an electrogram of the heart which is a
 graph of voltage versus time of the electrical activity of the heart using electrodes
 placed on the skin. These electrodes detect the small electrical changes that
 are a consequence of cardiac muscle depolarization followed by repolarization
 during each cardiac cycle (heartbeat). Changes in the normal ECG pattern occur
 in numerous cardiac abnormalities, including cardiac rhythm disturbances (such
 as atrial fibrillation and ventricular tachycardia), inadequate coronary artery
 blood flow (such as myocardial ischemia and myocardial infarction), and
 electrolyte disturbances (such as hypokalemia and hyperkalemia).