Arrhythmia is defined as Abnormality of rate, rhythm or site of origin of cardiac impulse or impulse conduction. It mainly causes by myocardial hypoxia/ischemia, electrolyte imbalance, trauma, and drugs. Antiarrhythmics are classified into sodium channel blockers, β-adrenergic blockers, K+ channel blockers, and Ca2+ channel blockers which are discussed briefly in this chapter. At the end of this chapter there are questions along with their crisp and to the point answers have been also given, which will be of benefit for answering the short answers and even a viva voce question.