For purposes of understanding the significance of electrical axis or axis deviation, the heart may be regarded as a strip of muscle. If the two electrodes of a galvanometer make contact at A and B of a muscle strip (fig. 1), and the current runs parallel to and in the plane of the electrodes, a deflection occurs. If the electrodes are at X and Y, the electrical fields at these points approach a balance, little or no difference of potential is present, and practically no deflection occurs. For purposes of simplification, contacts A-B may be likened to lead I, and points X-Y to lead III. If three leads are so arranged as to form an equilateral triangle, an idea of the position of the muscle strip may be obtained by comparing the height of the deflections in the three leads. In figure 2 A, it is noted that lead II