There are several underlying factors including anatomical substrates (coronary artery disease, cardiomyopathy, valvular disease, congenital heart disease, WPW syndrome) and modulating factors(autonomic nervous system, electrolyte balance, drugs) which may induce sudden cardiac death. Although studies evaluating mechanisms of sudden cardiac death are increasing, evaluation of risk of each patient and effectiveness of preventive treatments are still inadequate. Sudden death due to life threatening arrhythmias in the out-of-hospital situation can be resuscitated by non-medical staff with automated external defibrillator. In these resuscitated high-risk patients implantable cardioverter and defibrillator could be used to prevent sudden death due to unpreventable further arrhythmic episodes. Widespread availability of automated external defibrillator is mandatory.