In survivors of acute myocardial infarction (AMI), the restoration of anterograde flow in the infarct artery, even if accomplished beyond the time for myocardial salvage, may reduce the frequency of subsequent arrhythmic events and sudden death. Twelve subjects (8 men and 4 women, aged 39 to 69 years) with a first AMI, signal-averaged electrocardiographic late potentials, and an occluded infarct artery were prospectively identified. Seven (group I) had successful coronary angioplasty 6 to 15 days after AMI, and 5 (group II) were managed conservatively. Follow-up signal-averaged electrocardiography was performed 3 to 7 months later. From baseline to follow-up, the 7 group I subjects had a significant change in QRS duration (117 +/- 13 [mean + SD] to 102 +/- 10 ms), root-mean-square voltage (10.4 +/- 4.7 to 31.0 +/- 7.6 microV), and low-amplitude signal duration (47.5 +/- 8.5 to 32.4 +/- 5.2 ms) (p < or = 0.05 for all 3 variables). No group I patient had a late potential at follow-up. In contrast, the 5 group II patients showed no change in QRS duration or low-amplitude signal duration from baseline to follow-up, and all 5 had a late potential at follow-up. At follow-up, the root-mean-square voltage was significantly greater and the low-amplitude signal and QRS durations significantly less in group I than in group II (p < 0.05 for all 3 variables). Thus, in our patients, the mechanical restoration of anterograde perfusion in an occluded infarct artery 1 to 2 weeks after AMI caused the resolution of signal-averaged electrocardiographic late potentials.