PURPOSE: Exercise-induced myocardial perfusion abnormalities have been reported in patients with myocardial bridging, possibly by tachycardia-induced shortening of diastole. Dipyridamole TI-201 SPECT findings were evaluated in patients with myocardial bridging to assess perfusion abnormalities during dipyridamole stress. MATERIALS AND METHODS: Dipyridamole TI-201 SPECT images of 12 patients with myocardial bridging (> or = 50% systolic narrowing) were evaluated. The peak heart rate during dipyridamole stress was less than 110 beats/min in all patients. The control group was 118 patients with fixed left anterior descending artery (LAD) disease. RESULTS: Fourteen sites of systolic arterial narrowing were present in LAD: two in mid-LAD, seven in distal LAD, and five in septal branches. Dipyridamole TI-201 SPECT showed reversible perfusion defects in three of six sites with 50% to 70% systolic narrowing and seven of eight sites with more than 80% systolic narrowing. Overall, 71% (10 of 14) had a reversible perfusion defect. Five patients with septal branch compression had a perfusion defect in the midanteroseptal wall without an apical abnormality. In the control group, no patient had an isolated perfusion defect in the midanteroseptal wall or septal branch disease (5 of 12 compared with 0 of 118; P < 0.001). CONCLUSIONS: Perfusion abnormalities on dipyridamole TI-201 SPECT are observed in LAD or its branches in patients with high-grade myocardial bridging. Myocardial bridging may decrease coronary flow reserve but not necessarily via tachycardia. Isolated perfusion defects in the midanteroseptal wall may be a characteristic finding of septal branch compression, because a fixed lesion involving a septal branch only is rare.