The pharmacokinetics and haemodynamic effects of tocainide, an orally active structural analogue of lignocaine, were studied in patients with acute myocardial infarction complicated by left ventricular failure. Fourteen patients (mean age 65 years) with acute myocardial infarction complicated by mild left ventricular failure were studied, following a single dose of tocainide (250 mg) by intravenous infusion, over 30 min. Heart rate, systemic arterial pressure, pulmonary artery pressure and cardiac output were monitored. Plasma tocainide levels were estimated by gas chromatography. The mean plasma level of tocainide achieved was 2.95 micrograms/ml (15.37 mmol/l). The mean plasma half-life was 15.6 h. The mean cardiac index was reduced 5 min after completion of the infusion, from 2.24 1 min-1 m-2 (+/- 0.40) to 2.07 1 min-1 m-2 (+/- 0.29) (P less than 0.01). At 90 min the cardiac index had returned to pre-treatment levels. Small changes were seen in the heart rate, arterial blood pressure and the pulmonary artery pressure but these changes were not statistically significant. The pharmacokinetics of tocainide were not significantly altered in patients with acute myocardial infarction complicated by mild left ventricular failure.