An electrocardiogram, also called an ECG or EKG, is a simple test that detects and records the electrical activity of the heart. It is used to detect and locate the source of heart problems. An EKG is sometimes called a 12-lead EKG (or 12-lead ECG) because the electrical activity of the heart is most often recorded from 12 different places on the body at the same time. An EKG shows how fast the heart is beating. It shows the heart’s rhythm (steady or irregular) and where in the body the heartbeat is being recorded. It also records the strength and timing of the electrical signals as they pass through each part of the heart. It is the best way to measure and diagnose abnormal rhythms of the heart, particularly abnormal rhythms caused by damage to the conductive tissue that carries electrical signals, or abnormal rhythms caused by levels of salts, such as calcium, that are too high or low.