Encainide is an antiarrhythmic drug with class IC activity which has been used in the treatment of life-threatening ventricular arrhythmias, symptomatic ventricular arrhythmias and supraventricular arrhythmias. The antiarrhythmic activity is due to the parent drug and its two principal active metabolites, and in the extensive metabolising phenotype (90% of patients), metabolites are present in plasma at higher concentrations than encainide itself. Encainide produces little haemodynamic change in patients with left ventricular dysfunction and thus has considerable therapeutic potential in view of its efficacy in patients with ventricular tachycardia, premature ventricular complexes and the Wolff-Parkinson-White syndrome. However, this potential is reduced by a tendency for encainide to aggravate arrhythmia in a proportion of patients. At present there is no reliable method of identifying patients at risk for this potentially serious side effect. The most common non-cardiac side effects are dizziness and blurred vision which seldom necessitate withdrawal of treatment. Thus, encainide has proved effective in controlling ventricular tachyarrhythmias including those which have not been controlled by other antiarrhythmic drugs.