The aim of this study was to evaluate how heart rate variability changes during acute myocardial infarction (AMI) and whether this change is different in anterior and inferior AMI. For this purpose 10 patients with anterior (mean age 53 +/- 11 years) and 11 patients with inferior (mean age 55 +/- 11 years) AMI underwent 2 consecutive 24-hour Holter recordings (H1, H2) which started, at most, 6 hours after the onset of symptoms and a further two H at the 10th (H3), and 28th day (H4) of AMI. None of the patients suffered from diabetes or was taking beta-blockers. The standard deviation of the RR intervals (SDRR) for a 24-hour period was evaluated for each H in the group of patients with anterior and inferior AMI. In H1, SDRR was statistically lower in anterior compared to inferior AMI (64 +/- 20 versus 106 +/- 27; p < 0.0001). No statistically significant differences were found in H2 between the anterior and inferior AMI (72 +/- 19 versus 76 +/- 14), due to a reduction in SDRR in inferior AMI: from 106 +/- 27 in H1 to 76 +/- 14 in H2; p < 0.002. No statistically significant changes were present in anterior AMI patients between H1 and H2 (64 +/- 20 versus 72 +/- 19). SDRR recovers at H3 increasing in both groups (anterior: 101 +/- 28, p < 0.001; inferior: 108 +/- 29, p < 0.004). No further significant changes in SDRR were present at H4 for either group (anterior 117 +/- 30; inferior: 118 +/- 31).(ABSTRACT TRUNCATED AT 250 WORDS)