An electrocardiogram (ECG or EKG, abbreviated from the German Elektrokardiogramm) is a graphic produced by an electrocardiograph, which records the electrical activity of the heart over time. Its name is made of different parts: electro, because it is related to electronics, cardio, Greek for heart, gram, a Greek root meaning "to write".
The heart muscles create electrical waves when they pump. These waves pass through the body and can be measured by wires attached to the skin. Wires on different sides of the heart measure the activity of different muscles. An ECG displays the voltage of these wires, and the muscle activity that they measure from different directions. This display indicates the overall rhythm of the heart, and weaknesses in different muscles. It is the best way to measure and diagnose abnormal rhythms of the heart, particularly abnormal rhythms caused by damage to the nerves that carry electrical signals, or abnormal rhythms caused by levels of salts, such as calcium, that are too high or low. In myocardial infarction
(MI), the ECG can often identify the heart muscles that are damaged, but it's not sensitive enough to rule out certain kinds of damage. The ECG can also measure the pumping ability of the heart, although ultrasound
is more accurate.