Electrocardiography (ECG or EKG) is a diagnostic tool used to measure the electrical activity of the heart. It is used to detect abnormalities in the heart rhythm and to diagnose cardiac diseases. An ECG records the electrical activity of the heart as it contracts and relaxes. The recording is done by placing electrodes on different parts of the body, usually the chest, arms, and legs. The electrodes pick up small electrical signals that are generated by the heart muscle as it contracts and relaxes. The signals are then amplified and displayed on a monitor or printed out on paper. An ECG can be used to detect a variety of cardiac conditions including arrhythmias, coronary artery disease, heart attack, and congestive heart failure.