Ventricular arrhythmia observed in the acute stage of myocardial infarction is profoundly related to the autonomic balance. To investigate prediction of ventricular arrhythmia, heart rate variability and plasma catecholamine concentration were simultaneously measured for a week in 17 consecutive patients with first anterior or anteroseptal Q wave infarction treated without specific coronary intervention. The cross-sectional plot of coefficient of variance (= standard deviation of N-N interval/mean N-N interval x 100; %) as a function of plasma epinephrine on the day of admission remained lower than the standard average. Ventricular premature contractions increased in proportion to the plasma epinephrine concentration. In the first week of hospitalization, plasma epinephrine concentration and frequency of premature contraction decreased exponentially, whereas the coefficient of variance showed a modest decline. Ventricular tachycardia refractory to xylocaine with rate accelerating with persistence was observed only in patients with the peak epinephrine concentration > 375 pg/ml. Plasma epinephrine concentration rather than coefficient of variance during sleep after the first acute episode is more closely related to the following triggered ventricular arrhythmia.