Analysis of monitored electrocardiograms, recorded in 77 patients during the first 48 hours following the onset of myocardial infarction, revealed 492 episodes of ventricular tachycardia with rates of 90-220 min-1. Characteristics of the ventricular tachycardia episodes were correlated with heart rate and with the rate and complexity of ventricular arrhythmias in the 10-min period preceding ventricular tachycardia. Ventricular tachycardia with rates of 140-180 min-1 and with a QS configuration was the most frequent event. The first ectopic complex of VT was R-on-T in only 17.2%. Sinus tachycardia was associated with significantly fewer episodes of VT with rates of 110-140 min-1 than when the sinus rate was normal. However episodes of ventricular tachycardia with rates of 181 to 220 beats min-1 were more frequent during sinus tachycardia. Analysis of the frequency of premature ventricular contractions in the 10-min period immediately preceding ventricular tachycardia revealed no premature ventricular contractions in 24.4% of cases. Multiple premature ventricular contractions with a frequency of greater than or equal to 5 min-1 were observed in 8.4% of cases, multifocal in 30.3%, couplets in 24% and early PVCs in 12.2%. In the minute before ventricular tachycardia, only 40.2% of cases displayed premature ventricular contractions. In that minute, complex premature ventricular contractions were distributed as follows: multifocal in 10%, couplets in 8.7% and early PVCs in 2.6% of cases. Out of the total of 492 runs of ventricular tachycardia, 5 cases (1%) resulted in ventricular fibrillation.(ABSTRACT TRUNCATED AT 250 WORDS)