1. To investigate the effect of lignocaine upon coronary blood flow, myocardial systolic wall function and high energy phosphate stores, lignocaine was administered as a rapid intravenous injection to 14 open chest anaesthetized swine. 2. Before and after injection, measurements were made of coronary blood flow by electromagnetic flow probe, per cent wall thickening by ultrasonic crystals, adenosine triphosphate (ATP) and creatine phosphate (CP) content by myocardial biopsy, and arterial pressure by central aortic catheter. The animals were divided into two groups based on whether or not they received a continuous low-dose infusion of lignocaine prior to the study. Group I received the continuous low-dose infusion of lignocaine and group II did not. 3. With a 2 mg/kg lignocaine injection, peak diastolic coronary flow rose significantly in groups I and II by 27 +/- 7 and 29 +/- 7% respectively. This was followed by a significant decline in per cent wall thickening in groups I and II of -11 +/- 2 and -19 +/- 6% respectively. In group I myocardial CP content decreased after lignocaine injection by 58 +/- 6% and ATP tended to rise even though systolic and diastolic pressure did not change significantly. In group II neither CP nor ATP changed significantly, but systolic and diastolic blood pressure decreased significantly. 4. Repeat lignocaine injections were given over a wider dosage range (0.5-4.0 mg/kg) to determine dose-response for lignocaine versus coronary blood flow. Coronary blood flow increased and per cent wall thickening decreased as doses of lignocaine were increased. 5. It was concluded that rapid intravenous lignocaine injection appeared to cause a dose-dependent coronary dilatation and systolic dysfunction. Pre-treatment with low-dose continuous infusion of lignocaine appeared to result in a decrease in CP and a rise in ATP when compared with no pre-treatment--despite a similar effect on myocardial function and coronary blood flow.