An electrocardiogram (ECG) is one of the simplest and fastest tests, used to evaluate the heart. Electrodes are placed at certain spots on the chest, arms, and legs. The electrodes are connected to an ECG machine by lead wires. the electrical activity of the heart is then measured, interpreted, and printed out it is used to look for the cause of chest pain and also to evaluate problems that may be heart-related like to identify irregular heartbeats.