This book delineates the state of the art of the diagnosis and treatment of J wave syndromes, as well as where future research needs to be directed. It covers basic science, translational and clinical aspects of these syndromes. The authors are leading experts in their respective fields, who have contributed prominently to the literature concerning these topics.J wave syndromes are one of the hottest topics in cardiology today. Cardiac arrhythmias associated with Brugada syndrome (BrS) or an early repolarization (ER) pattern in the inferior or infero-lateral ECG leads are thought to be mechanistically linked to accentuation of transient outward current (Ito)-mediated J waves. Although BrS and ER syndrome (ERS) differ with respect to magnitude and lead location of abnormal J waves, they are thought to represent a continuous spectrum of phenotypic expression termed J wave syndromes.