Several previous studies suggest that myocardial bridging (MB) is associated with ischemia and rhythm disturbances. We sought to examine exercise-induced changes in P wave duration and dispersion (PWD), the markers of atrial conduction abnormalities in patients with isolated MB of left anterior descending artery (LAD) and control subjects. Eighteen patients with MB of LAD (group-I) and 22 subjects with angiographically demonstrated normal coronary arteries (group-II) underwent treadmill exercise testing. Before and after exercise ECG was recorded at a paper speed of 50 mm/s. The change in maximum and minimum P wave duration was measured manually and difference between two values was defined as PWD. There was no difference between two groups in terms of demographic properties. Baseline maximum and minimum P wave duration and PWD durations were similar in both groups and they did not change after exercise. (Group-I: before and after test; 114 +/- A 10 vs. 114 +/- A 9, 66 +/- A 13 vs. 67 +/- A 10, and 47 +/- A 9 vs. 45 +/- A 13 ms, P > 0.05, group-II; 113 +/- A 9 vs. 115 +/- A 8, 68 +/- A 11 vs. 68 +/- A 11, 45 +/- A 11 vs. 48 +/- A 15 ms for each, respectively). In addition there was no significant correlation between PWD and P wave duration and echocardiographic variables. In patients with MB of LAD, PWD and P wave duration were not different than healthy subjects and treadmill exercise testing did not induce atrial conduction abnormalities in both groups.