Placement of ECG electrodes, illustration. Electrocardiography is a diagnostic procedure used to record the electrical activity of the heart. There are 10 electrodes used for a 12-lead ECG: four limb leads (RA, right arm; LA, left arm; RL, right leg; LL, left leg) and six precordial (chest) electrodes (V1 to V6). The chest electrodes placements are: V1 in the fourth intercostal space (between ribs 4 and 5) just to the right of the sternum (breastbone); V2 at the same level the other side of the sternum; V4 in the fifth intercostal space on the mid-clavicular line; V3 between V2 and V4; V5 and V6 level with V4, on the left anterior axillary line and the mid-axillary line respectively.