Background: It has been known that specificity of myocardial perfusion scintigraphy in patients with bundle branch block (BBB) is significantly low. In this study, we aimed to exam the diagnostic value of ECG gated ^99mTc-myocardial SPECT and to evaluate the role of myocardial performance measurement in conjunction with myocardial SPECT to improve diagnostic accuracy in BBB patients. Method: Total 186 patients of BBB (n=79), post myocardial infarction (MI, n=59) and healthy hypertension patients (n=48) were enrolled. Patients with BBB (mean age 68짹9 years, Left BBB (n)=40 and right BBB (n)=39) who had taken both stress-rest SPECT using ^99mTc compounds and coronary angiography were evaluated. For the patients who showed false positive results on SPECT, we measured the myocardial performances using 2D-speckle tracking echocardiography. The myocardial performance measurements in BBB are compared with both healthy subjects except hypertension and post MI patients. Results: There were 70 (88.6%) BBB patients who diagnosed as having perfusion defect without significant stenosis (diameter stenosis >50%) on coronary angiography. The specificity of ^99mTc-SPECT in this study was 11.4%. Significant number (97.1 %) of patients with false positive results showed fixed perfusion defect. 85% of LBBB patient showed anterior and/or septal wall and 35.9% of RBBB patient showed inferior wall perfusion defect. The ejection fraction of both BBB patients and post MI patients (52짹11% vs. 47짹13 %, 0=0.54) was significantly low compared with hypertension patients (vs. 65짹7%, p<0.001). However, there were significant differences in global longitudinal strain (LS) value among three groups (-15.9짹5.3 (BBB) vs. -13.2짹5.0 (post MI) vs. -18.6짹3.4 % (Hypertension), p<0.001). Also, the LS of basal lateral segment was significantly high in BBB patients compared with post MI patients (-18.1짹6.2 vs. -13.7짹7.1%, p=0.038) without significant differences compared with hypertension patients (vs. -18.9짹6.3%, p=0.661). Conclusion: Our data shows significantly low specificity of stress-rest ^99mTc-SPECT in BBB patients. The diagnostic accuracy for detect false positive perfusion defect could be improved by myocardial performance measurement in conjunction with myocardial perfusion scintigraphy in BBB patients.