PURPOSE: Thallium single photon emission computed tomography(SPECT) has been known as its high incidence of false positive result, even though quantitative perfusion SPECT scans have advantage in differentiating attenuation artifacts from true perfusion defects. Dyssynchrony is one of the causes of false positive result of SPECT and by normal QRS duration, dyssynchrony cannot be excluded. We aimed this study to evaluate the dyssynchrony might be a reason for false positive results of myocardial SPECT in stable angina patients. METHODS: 85 patients with clinically diagnosed stable angina and positive myocardial SPECT results who underwent coronary angiogram were included. These patients were divided into two groups(group I, patients with positive SPECT results and normal coronary angiography(n=47, mean age=69.4짹5.8 years, 20 males), group II patients with positive SEPCT results and significant coronary lesion in coronary angiography(n=37, mean age=71.1짹4.3 years, 20 males). We examined conventional echocardiographic parameters and dyssynchrony index including septal to posterior wall motion delay on parasternal long axis view, both inter-ventricular and intra-ventricular electromechanical delay, opposite wall motion delay on apical 4 chambes view, 2 chambes view and long axis view. RESULTS: There were no significant differences in anteroseptal and posterior wall time delay (basal segment: 55.9짹53.2 vs. 43.1짹40.0, P=0.223, mid segment; 60.9짹54.4 vs. 53.0짹53.6msec, P=0.505). But the basal segment time delay between lateral and septal wall peak systolic velocity (BS-BL) were significantly delayed in group I (59.2짹53.8 vs. 36.4짹36.0 P=0.022). Also, time delay between anterior and inferior wall was significantly different in mid segment(MA-MI)(basal segment: 45.3짹39.0 vs. 30.1짹34.4, P=0.065, mid segment; 68.4짹52.9 vs. 43.1짹37.6msec, P=0.012). By receiver operation curve analysis, the area under the curve to predict false positive SPECT results was 0.792 and 0.792 in BS-BL and MA-MI respectively. The optimal cutoff time delay values to predict false positive SPECT result were 11.5msec and 19.5msec in BS-BL and MA-MI. CONCLUSIONS: Myocardial SPECT examination with dyssynchrony index measurement might be good tool for screen possible normal coronary angiographic results.