Bonnecor was tested for its antiarrhythmic activity in patients with acute myocardial infarction in the first 24 hours of the disease complicated by arrhythmias as ventricular premature beats (VPB). Proceeding from the comparison of its clinical efficiency and pharmacokinetic parameters in 38 patients, the optimal dosage of the drug was formulated. When given intravenously to the patients in dose of 25-37.5 mg bonnecor produced 92% antiarrhythmic responses, failed to shorten heart rate and to lower blood pressure; the agent led to a prolonged P-Q interval as evidenced by ECG. The antiarrhythmic activity, the dose of the drug, and its plasma concentration were found to be closely related. The mean effective bonnecor concentration was ascertained to be 0.45 +/- 0.24 micrograms/ml.