A number of antiarrhythmic agents have been used for both rhythm and rate control strategies in the patients with atrial fibrillation. One of the limitations in pharmacological management is the occurrence of proarrhythmias including torsades de pointes (Tdp) associated with drug-induced QT prolongation by class Ia and class III agents. The clinical characteristics, predisposing factors and the management of Tdp ventricular tachycardia (VT) are discussed in this section. Another lethal proarrhythmia is wide-QRS (sine-wave-shaped) VT which results from strong Na channel blocking effect of class Ic agents. Various bradyarrhythmias including sinus node dysfunction and AV conduction disturbance are sometimes observed during pharmacological treatment of atrial fibrillation, and may require cessation of drug use or permanent pacemaker implantation.