Sudden cardiac death (SCD) is defined as unexpected natural death from cardiac causes heralded by abrupt loss of consciousness within 1 hour from the onset of symptoms. Most consensus documents define sudden as death that occurs within 1 hour or less from the onset of symptoms or that occurs during sleep. Ventricular fibrillation (VF) is the major arrhythmia responsible for SCD, but bradyarrhythmias also play a minor role. Although the exact mechanism of VF is unknown, focal source and reentrant mechanism are shown to be responsible for initiation and maintenance of VF. VF is initiated and perpetuated by the interplay of several factors including tissue heterogeneity, wavebreaks due to disorder of impulse conduction, restitution properties of myocardium, cardiac memory, altered intracellular Ca+ transients along with repolarization alternans and autonomic imbalance. Malignant ventricular arrhythmias are the major offenders for SCD.