The objective of the submitted work was to assess, using programmed stimulation of the cardiac ventricles during antiarrhythmic treatment (amiodarone and propafenon administered orally), the presence of indicators suggesting imminent ventricular ectopic proarrhythmia. The authors included in the group, after elimination of subjects with ECG (Holter monitoring) signs of proarrhythmias 50 patients (43 men, 7 women, 23-78 years, mean age 54.0 +/- 14.2 years), where they used initial programmed stimulation of the ventricles, not sooner than three months after acute cardiac disease. On account of electric instability of the ventricles the authors administered to 39 patients amiodarone by the oral route (200 to 400 mg/day) and to 11 subjects propafenon also by the oral route (900 mg/day). A subsequent programmed stimulation of the ventricles was repeated after amiodarone treatment after an interval of 4-144 weeks and after propafenon treatment after 1-48 weeks. They included among indicators of proarrhythmic action of antiarrhythmics (as compared with the initial examination): induction of diagnostic tachycardia at a lower grade of stimulation or with a smaller number of extrastimuli, the change from non-persisting unimorphous ventricular tachycardia into permanent unimorphous ventricular tachycardia, an increase of the frequency of tachycardia, marked deterioration of the patient's symptoms during tachycardia and the necessity to eliminate tachycardia by an electric discharge (during the initial examination an electric discharge was not used). The authors described in the group on indicator of proarrhythmic effect conditioned by programmed stimulation of the ventricles in 24 patients (48%). In one subject they found simultaneously two indicators in 12 instances (24%) and three indicators in 5 instances (10%).(ABSTRACT TRUNCATED AT 250 WORDS)