Calcium antagonists such as verapamil/diltiazem predominantly delay av-nodal conduction. Thus, the most important clinical indications for their application are the av-nodal-reentrant-tachycardia as well as the slowing of rapid ventricular response in intraatrial tachyarrhythmias. To reestablish sinus rhythm in atrial fibrillation, verapamil should be combined with chinidin. Usually, ventricular arrhythmias cannot be suppressed by calcium antagonists, but they may be indicated in exercise-induced ventricular arrhythmias and tachycardias arising from the right ventricular outflow tract. Verapamil/diltiazem are effective in ischemia-induced tachyarrhythmias, especially ventricular fibrillation, because of the reduction of ischemia-related conduction delay in the ischemic zone. The effectiveness of calcium antagonists in the secondary prevention of myocardial infarction can not yet be definitively defined.