Supraventricular and ventricular arrhythmias are extremely common in cardiac failure. No antiarrhythmic agent has been shown to improve survival in atrial fibrillation with left ventricular systolic dysfunction. In symptomatic ventricular tachycardia or fibrillation, treatment is generally determined by the ejection fraction (low EF: amiodarone; intermediate EF: amiodarone and/or betablocker; normal EF: most antiarrhythmics active at ventricular level). In asymptomatic ventricular arrhythmias, the prescription of antiarrhythmic drugs should be restrictive as few studies have demonstrated any benefits and the pro-arrhythmic effects are dangerous. No medication has been shown to be of real value in ventricular tachycardia complicating hypertrophic cardiomyopathy.