Abstract:The hemodynamic effects of lidocaine given as bolus injections and by infusion were studied in 19 anesthetized dogs before and after acute myocardial infarction produced by a two stage ligation of coronary arteries. The infarcted tissue represented an average of 36.2% of the weight of the left ventricle. Lidocaine infusion at a rate of 200 &mgr;g/kg/min produced significant elevations of left ventricular dp/dt, cardiac output, and systolic left ventricular and aortic pressures before experimental myocardial infarction, with significant elevations in cardiac output only, following the coronary artery ligation. Prior to myocardial infarction bolus injections of 5 mg/kg lidocaine resulted in decreases in left ventricular systolic and aortic pressures, left ventricular dp/dt, cardiac output, heart rate and systemic vascular resistance lasting approximately five minutes. After coronary artery ligation the same dose of lidocaine produced more prominent circulatory changes of longer duration, including elevation of left ventricular diastolic and left atrial pressures. It is concluded that large doses of lidocaine given as a single injection can produce significant circulatory depression in a heart compromised by myocardial infarction.