To understand the electrical forces in the horizontal plane, it is important to become familiar with the exact placement of the precordial leads as illustrated above. V1 is in the 4th intercostal space just to the right of the sternum and V2 is in the 4th intercostal space just to the left of the sternum. V4 is in the 5th left intercostal space at the midclavicular line. V3 is half way along a straight line between V2 and V4. V5 and V6 are at the same level as V4 with V5 in the anterior axillary line and V6 in the mid axillary line.