Late ventricular potentials (LVP), heart rate variability (HRV) and dispersion of QT interval (QTd) were studied in 91 patients with myocardial infarction with various ventricular arrhythmias. Patients with episodes of sustained ventricular tachycardia (group 4) had the following characteristics: prevalence of LVP 73.7%, QTd 82.5 ms, standard deviation of RR intervals (SD) 26.5 ms; spectral analysis of HRV revealed preponderance of sympathetic influences and lowered vagal activity. Frequency of LVP detection, QTd and SD in patients with ventricular extrasystoles (Lown classes 3-5) (group 3) were 33.3%, 72.8 ms, and 42.8 ms, respectively. Patients of group 3 also had augmented sympathetic and lowered parasympathetic influences. These data significantly differed from those obtained in patients with Lown class 1-2 ventricular extrasystoles (group 2) and patients without extrasystoles (group 1). Groups 3 and 4 had significantly different prevalences of LVP and values of some HRV parameters but similar QTd. There was close correlation between presence of severe ventricular arrhythmias and some parameters of HRV and signal averaged ECG. Stepwise regression analysis showed that the following group of parameters was related to the presence of malignant ventricular rhythm disturbances: heart rate, SD and total QRS duration (p<0.05). Thus patients with life threatening ventricular arrhythmias were characterized by the presence of LVP and changes of some parameters of HRV and QTd. Registration of these parameters can apparently be used for prediction of potentially fatal ventricular arrhythmias in patients with myocardial infarction.