Mexiletine is a new local anaesthetic antiarrhythmic agent whose chemical structure and electrophysiological properties closely resemble those of lignocaine although its anticonvulsant and pharmacokinetic properties differ from that drug. Unlike lignocaine (lidocaine) it is active following oral administration with a plasma half-life varying between 8 and 20 hours so that it can be administered twice or three times daily to sustain therapeutic plasma levels. The drug is effective when given intravenously or by the oral route in controlling ventricular arrhythmias especially following acute myocardial infarction but the side effects are greater during parenteral administration. Side effects during chronic oral therapy with mexiletine have not posed a serious problem. Mexiletine has the pharmacodynamic and pharmacokinetic properties of an agent suitable for the chronic oral prophylaxis of serious ventricular arrhythmias in patients with ischaemic heart disease.