Myocardial bridging (MB) of coronary arteries has been considered as an incidental angio-graphic finding; however, several reports suggest its association with angina pectoris, myocardial ischemia, and even infarction. In this study the authors aimed to assess exercise-induced QRS changes in patients with isolated MB and to compare those with coronary artery disease (CAD) and healthy subjects. The study population consisted of 17 patients with angiographically proven MB (group 1), 16 patients with left anterior descending (LAD) artery stenosis (group 2), and 14 healthy subjects (group 3). Each subject underwent treadmill exercise testing according to Bruce protocol. In each subject amplitude of the Q, R, and S waves in leads aVF and V(5) was measured manually before and immediately after exercise. The Athens QRS score was calculated by subtracting the Q-, R-, and S-wave differences in leads aVF and V(5). Baseline characteristics of each group were similar. There was no difference among the groups with respect to exercise testing parameters (peak heart rate, blood pressure, test duration, etc). In group 1, ST-segment depression ratio was found to be higher than that of group 3 but lower than that of group 2. In group 1, exercise QRS score was found to be lower than that of group 3 while it was higher than that of group 2 (2.9 +/- 2.3 vs 6.5 +/- 3.2 p = 0.001 and 2.9 +/- 2.3 vs 2.6 +/- 2.4 p = 0.001, respectively). In patients with MB exercise, QRS score was significantly lower than in those with normal coronary flow while it was higher in those with CAD. This may result from exercise-induced ischemia at the area perfused by the bridged artery.