An arrhythmia is a disorder of the heart that results in an erratic or absent heart rhythm. Arrhythmias are described in two broad categories: bradyarrhythmias (abnormally slow rhythms) and tachyarrhythmias (abnormally fast rhythms). Bradyarrhythmias are caused by the heart's failure to generate electrical signals or by a disorder in the conduction system of the heart. Tachyarrhythmias are either caused by conduction anomalies in the heart that allow heartbeats to circulate along abnormal pathways (reentry) or by auxiliary pacemakers in the heart that initiate abnormal activity (ectopy). Bradyarrhythmias are generally treated with drugs and pacemakers. Tachyarrhythmias are treated through drugs, implantable cardioverter defibrillators, and catheter ablation.