In 848 coronary arteriograms performed in a two-years period 21 patients (2.5%) showed a myocardial bridging of the left anterior descending artery. Resting- and/or stress-ECG were abnormal in half of the patients. Regional lactate-metabolism measured in the great cardiac vein at rest and during maximal atrial pacing was normal (29 +/- 12 resp. 24 +/- 9%). Thermodilution of great cardiac vein bloodflow at rest and during atrial pacing also demonstrated normal values (94 +/- 33 resp. 138 +/- 30 ml/min). Biphasic 201-Thallium myocardial imaging revealed no case of reversible perfusion defect, but surprisingly frequent (5 of 16 patients) clearly irreversible defects limited to the interventricular septum. We conclude that muscle bridges do not cause myocardial ischemia at rest or during exercise.