What Is It?
An electrocardiogram (EKG) is a painless process that records the heart's electrical activity. Small metal electrodes are placed on the person's wrists, ankles and chest. The electrical signals travel from the electrodes through wires to the EKG machine, which transforms the signals into patterns or waves. Different waves represent different areas of your heart through which electrical currents flow. The electrical currents stimulate the heart muscles to contract and relax. The P wave represents the current in the upper chambers of the heart (atria); the QRS complex represents current in the lower heart chambers (ventricles); and the T wave represents the heart's brief "rest period" as it recharges electrically (repolarizes) between heartbeats.
EKG waves are recorded on paper as they move through the EKG machine, showing the heart rate and heart rhythm. The appearance of the wave patterns can give important clues about damage to the heart muscle or irritation of the membrane around the heart (pericardium).