This book provides clinical and electrovectorcardiographic evidence of the existence of left septal fascicular blocks and demonstrates the clinical importance of these blocks in the clinical scenario of acute coronary syndrome. There are currently no standard criteria for detecting conduction defects involving the third left fascicle, the septal or median fascicle, and the very existence of such defects is still a matter of controversy. This book provides acceptable and consistent terminology and definitions for the electrovectorcardiographic diagnosis of a left septal fascicular block. Left Septal Fascicular Block: Characterization, Differential Diagnosis and Clinical Significance is an original and unique book that sheds light on an important topic of discussion in cardiac electrophysiology.