The article discusses the comparative antiarrhythmic effectiveness of trimecaine and lidocaine in patients with acute myocardial infarction in the first 24 hours of the disease. The 45 patients included in the study were separated into 3 groups: the 1st (control) group consisted of 15 patients with acute myocardial infarction who were not given antiarrhythmic or arrhythmogenic agents; the 2nd group was formed of 15 patients who from the time of admission were given trimecaine by intravenous drip at a rate of 2 mg/min for purposes of prevention after preliminary jet-injection of 80 mg of the drug; the 3rd group consisted of 15 patients given lidocaine by the same schedule. An antiarrhythmic effect was noted in 60% of group 2 patients and in 87% of group 3 patients. No antiarrhythmic effect was produced in 40% of patients treated with trimecaine and in 13% of those given lidocaine.