Sudden cardiac death (SCD) is caused by lethal ventricular arrhythmias, i.e. ventricular fibrillation (VF) and sustained ventricular tachycardia (VT). Ischemic heart diseases such as acute coronary syndrome and vasospastic angina are main cause of VT/VF leading to SCD. Other underlying heart diseases for VT/VF include cardiomyopathy (CM) such as hypertrophic CM (HCM), dilated CM (DCM), and arrhythmogenic right ventricular CM (ARVC). Inherited arrhythmias such as congenital long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia and early repolarization syndrome are another cause of VT/VF, and account for 1 – 2% of SCD in Western countires and approximately 10% in Japan. In this ACC-JCS Joint symposium, experts from two societies will present their own experience or data, and provide a comprehensive discussion for pathogenesis, prediction and prevention of SCD in a variety of underlying heart diseases.