The autonomic nervous system plays a critical role in triggering ventricular arrhyhmia and sudden death early after acute myocardial infarction. This study was designed to determine whether or not vagal and sympathetic responses are impaired after myocardial infarction and to evaluate the utility of physiologic stress tests for assessing autonomic dysfunction after myocardial infarction.

8 male patients with acute myocardial infarction(Group A) and old myocardial infarction(Group B) were studied with 8 control subjects of coinciding age and sex. 5 physiologic stress tests(deep breathing, sudden standing, Valsalva maneuver, ice bag application on the face, 70° headd-up tilt test) were performed.

1) Variation in heart rate during deep breathing, Standing-up, Valsalva maneuver, and ice bag application on the face was less in Group A than in Group B or Group C.

2) There was no significant difference in variation of heart rate between Group B and Group C.

3) Variation in heart rate caused by 70° tilt was not significantly different among the three groups.

Early after myocardial infarction, parasympathetic responses were significantly impaired, whereas sympathetic responses remained intact. Heart rate variability using physiologic stress test may be provide a means of detecting autonomic dysfunction after acute myocardial infarction.