The objective of this study was to assess the degree of QT dispersion and effect of thrombolytic therapy on QT dispersion in elderly (age > or =65 years) versus younger (age <65 years) patients with acute myocardial infarction. The QT dispersion was measured manually in 10 +/- 2 leads of 12-lead electrocardiograms on admission, at completion of thrombolytic therapy, and at day 2 after thrombolytic therapy in 36 elderly (73 +/- 5.7 years) and 36 younger (59.9 +/- 7.7 years) patients with acute myocardial infarction. Before initiation of thrombolytic therapy, elderly patients had higher absolute and corrected QT dispersion than younger patients (absolute QT dispersion: 76.3 +/- 7.3 versus 69.6 +/- 7.5 milliseconds, respectively, P < 0.0001; corrected QT dispersion: 77.9 +/- 7.6 versus 70.8 +/- 7.4 milliseconds, respectively, P < 0.001). The difference in QT dispersion between elderly and younger patients persisted at the completion of thrombolytic therapy (absolute QT dispersion: 75.1 +/- 7.2 versus 69.1 +/- 8.4 milliseconds, respectively, P = 0.001; corrected QT dispersion: 77.2 +/- 7.2 versus 70.7 +/- 8.0 milliseconds, respectively, P = 0.001) and at day 2 after thrombolytic therapy (absolute QT dispersion: 74.1 +/- 8.2 versus 69 +/- 9.1 milliseconds, respectively, P = 0.01; corrected QT dispersion: 76.0 +/- 7.9 versus 70.5 +/- 8.8 milliseconds, respectively, P = 0.006). Compared with the prethrombolytic values, there was no significant change in absolute and corrected QT dispersion at the completion of thrombolytic therapy or at day 2 after thrombolytic therapy in elderly or younger patients. Elderly patients with acute myocardial infarction have higher QT dispersion than younger patients with acute myocardial infarction, and QT dispersion does not change early after thrombolytic therapy in elderly or younger patients.