The authors discuss the aetiological, electrophysiologic and diagnostic problems pertinent to peripheric blocks. Using the current ECG and VCG tests, it is often difficult, and sometimes impossible, to identify the ventricular wall affected by the block, the intraparietal localization and the seat of the block. Purkinje fibres, junction or muscle fibres. Because of the scarcity of experimental data, some of the diagnostic-differentials exposed have more the feature of logical hypothesis than that of certainty. The commonly held concept that the peripheric blocks do not alter, but that the terminal phases of ventricular depolarization do, is confirmed. The initial phases can also be altered, in that the Purkinje-junction-muscular fibres may be damage even in the septum, while the large ducts of conduction remain undamaged. Several discrepancies found between the presence of electric patterns of septal necrosis and that of infarctions in autopic examinations can possibly be explained as peripheric blocks localized in the left septum.