A study about signal-averaged ECG in two groups: 73 patients with acute myocardial infarction and the control group of 56 people without heart disease (age, sex and anthropometric indicators almost equivalent) showed: In the first group (with MI): the ratio of the late potentials (LP) (+) were 38.36 percent, of late potentials (-) were 61.64 percent. In the control group: 100 percent of the patients with late potentials (-). The value of HFQRS (107.50 + or - 22.31 ms) and LAHF (53.39 + or - 15.13 ms) in LP (+) groups were higher than that in the LP (-) group, and RMS 40 (10.64 + or - 5.00 uV) were lower than that in the group LP (-) (with p 0.001). Early coronary intervention can reduce the incidence of late potentials (+). In patients with late potentials (+): 30.43 percent of ventricular arrhythmias.