The CAST studies have shown that class I antiarrhythmic agents cause an increase in mortality in patients with ventricular tachyarrhythmias after myocardial infarction. This led to an increase in the use of class III agents. The most important class III antiarrhythmic substances are amiodarone and sotalol. Since these drugs also have partially serious side-effects and drug interactions, the search for more effective and safer antiarrhythmics focuses on new class III drugs. These include, for instance, dofetilide, ibutilide, sematilide, clofilium, tedisamil and d-sotalol. None of these compounds, however, is yet available for broad clinical use. This is probably due to the fact that these new drugs, too, have various disadvantages, e.g. reverse use dependence and proarrhythmic effects.