Aim. To study the effects of trimethasidine on the specific features of arrhythmias, on the parameters of cardiac rhythm variability (CRV) and ischemic changes in the ST segment in patients with functional classes II-III chronic heart failure (CHF). Material and Methods. Twenty male patients with less than 45% left ventricular ejection fraction were examined. After stabilizing their status and working through basic therapy for a week, the patients were randomly divided in ftvo subgroups equally and followed up in the outpatient setting for 6 months. During two 3-month periods, they alternately received either the standard basic therapy or the standard therapy in combination with trimethasidine in a dose of 20 mg thrice a day. Hotter monitoring was performed before and 3 and 6 month after the therapy. Results. In patients with CHF on trimethasidine, there was a significant reduction in the number of paroxysms of ventricular tachycardia and high-grade ventricular extrasystoles, and a significant improvement of cardiac rhythm variability. Concurrently, a significant decrease in the frequency of episodes of ST-segment depression was recorded at ECG. Conclusion. Trimethasidine treatment in CHF patients induced a reduction in the incidence of cardiac rhythm disturbances, which may be associated with its antiischemic effect on the myocardium and, possibly, with the positive effect of cytoprotective therapy on autonomic tone.