Myocardial bridges have been associated with clinical and metabolic evidence of ischemia, although the mechanism for this is unclear. We measured coronary blood flow and segmental function at different heart rates prior to and after release of a myocardial bridge involving the left anterior descending coronary artery in a patient with angina. Before lysis of the bridge, atrial pacing was associated with a decreased systolic flow/total flow, increased duration of systole, a lag in diastolic flow, and functional deterioration. After release of the bridge, pacing was associated with increased systolic flow/total flow and systolic interval, no diastolic flow lag, and no functional deterioration. These data imply that before bridge division, systolic flow and the initiation of diastolic flow were impeded. Functional abnormalities resulting from the flow discrepancies at heart rates of 120 to 150 beats per minute may have accounted for this patient's symptoms.