It is not known if QT dispersion is useful for detecting coronary artery disease. We investigated whether QT dispersion at baseline and during adenosine triphosphate (ATP) infusion correlate with the imaging patterns obtained from ATP stress thallium-201 single-photon emission computed tomography (ATP-SPECT). QT dispersion was determined in 169 patients who underwent ATP-SPECT from 12-lead electrocardiograms obtained at baseline and 3 minutes after the beginning of ATP infusion. Based on the results of ATP-SPECT, patients were divided into 4 groups: normal (n = 55), ischemia (n = 38), ischemia and scar (n = 42), and scar (n = 34). Baseline QT dispersions (mean ± SD) in the normal, ischemia, ischemia and scar, and scar groups were 48 ± 15, 50 ± 17, 69 ± 25, and 70 ± 24 ms, respectively. Baseline QT dispersion was significantly greater in the groups with myocardial scar. QT dispersions during ATP infusion were 43 ± 16, 63 ± 20, 76 ± 20, and 62 ± 25 ms in the normal, ischemia, ischemia and scar, and scar groups, respectively. QT dispersion increased with ATP infusion in patients with myocardial ischemia. QT dispersion at baseline and during ATP infusion correlated with the ATP-SPECT imaging pattern. These findings suggest that baseline QT dispersion and ATP-induced changes in QT dispersion may help detect the presence of myocardial ischemia and scar.