Cardiac arrhythmias are cardiac rhythm disorders that comprise an important epidemiological and public health problem. Cardiac arrhythmias are significantly associated with increased risks of cardiovascular complications and sudden death, consequently leading to decreased quality of life, disability, high mortality, and healthcare expense. Atrial fibrillation (AF) is the most common sustained arrhythmia, and has been further increasing with the aging of society. Although the prevalence is relatively lower in Asians than in Westerners, the prognostic impacts on stroke and mortality in Asians are comparable. Sudden cardiac death (SCD) occurs in approximately 40 cases per 100,000 persons annually in each country of Asia. Most cases are caused by myocardial infarction and ventricular fibrillation in out-of-hospital cardiac arrest cases, but the proportion of myocardial infarction is lower in Asia than in Western countries. The primary electrophysiological disorders related to channelopathies, such as long QT syndrome, short QT syndrome, Brugada syndrome, early repolarization syndrome, and catecholaminergic polymorphic ventricular tachycardia, are estimated to be responsible for 10% of SCDs. Implantable cardioverter-defibrillator implantation has become established as an effective secondary prevention for SCD, and numbers have been increasing annually worldwide. New insights into arrhythmic diseases have been emerging from epidemiological, clinical, and genetic research, and contribute to improvements in diagnosis and prognosis.  (Circ J 2013; 77: 2419–2431)