An electrocardiogram, also called an EKG or ECG, 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 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. EKGs are used to evaluate signs and symptoms that could indicate heart problems. Many heart problems change the electrical “signature” of the heart in distinct ways. EKG recordings of this electrical signature can help reveal these heart problems. During an EKG, electrical signals in the heart are detected by electrodes placed on the skin. A machine records them on graph paper or displays them on a screen. An EKG is painless and harmless, and usually takes about 10 minutes to complete. Special EKG tests are done to detect certain kinds of heart symptoms, such as those that are present for only a few minutes out of the day, or that happen only while a person is exercising.