Septal necrosis + peripheral left blocks. Because of an extensive septal necrosis, the manifestation of the initial ventricular activation forces decreases in the precordial leads. With left bifascicular block (LASB + LPSB), the first ventricular activation forces become more evident and the electrical signs of septal necrosis can be concealed. In the presence of a trifascicular block, manifestation of the first ventricular electromotive forces diminishes again and the electrical signs of septal necrosis become evident once more. Small Q waves are present in leads V1 to V4. Extensive anterior necrosis + peripheral blocks. This necrosis is manifested by QS complexes from V2 to V6. An associated left bifascicular block reduces the electrical manifestation of dead tissue: QS complexes persist only in V3 and V4. In turn, a coexisting trifascicular block causes the presence of QS complexes from V2 to V5. Posteroinferior necrosis + peripheral blocks. Electromotive forces of the ventricular activation shift upward, due to a posteroinferior necrosis and QS or QR complexes are recorded in leads aVF, II and III. An associated left bifascicular block displaces the main electromotive forces downward, posteriorly and to the left, due to a delay of the posteroinferior activation fronts. The ventricular complexes become positive and wider in all leads, reflecting the potential variations of the inferior portions of the left ventricle: aVF, II, III, sometimes V5 and V6. Consequently, the electrical signs of necrosis are reduced or abolished. Due to a trifascicular block, wide and slurred QS complexes are recorded in aVF, II, III and sometimes in V5 and V6.