Abstract The electrocardiogram as shown by the evidence presented above, is a record of events in favored rather than in all regions of the heart. It registers the play of electromotive forces set up from moment to moment in these favored spots rather than the balance of the electromotive forces set up in the entire heart. It gives the order of invasion and retreat in these favored regions and depicts disturbances in these processes, primarily as they affect these favored regions. Similarly, it reveals injury currents affecting these particular regions but misses injury currents in other regions not so favorably situated. The precordial leads are from this viewpoint a method of bringing out into the open lesions in regions of the heart which are not favorably situated for notice by the ordinary distant leads.