ABSTRACT Background: The presence of left bundle branch block (LBBB) represents a major challenge in the non-invasive diagnosis of coronary artery disease (CAD), as demonstrated by primary tests including resting, stress electrocardiography (ECG) and stress echocardiography, which have conferred low diagnostic sensitivity and specificity. Thus, coronary angiography is usually required to confirm diagnosis. The aim of this study was to investigate the predictors of C AD among patients with LBBB and identify different ECG features of ischemic LBBB. Methods: This was a retrospective descriptive study of the records of patients from Zagazig University Catheterization Laboratory, Egypt, from May 2019 to May 2022. Among 3000 patients who underwent elective coronary angiography, only 168 patients (5.6%) had LBBB in a preprocedural 12-lead ECG. Patients with LBBB were classified according to presence of CAD on coronary angiogram into: Group I: Includes 96 patients with LBBB and CAD, 72 males and 24 females (mean age 60.9±4.2 years) which further was classified according to left ventricular ejection fraction (LVEF) into 2 subgroups: Subgroup A: with LVEF <50% and Subgroup B: with LVEF ≥50%. Group II: Includes 72 patients with LBBB without CAD, 42 males and 30 females (mean age 57.1±5.7 years). All patients with LBBB were reviewed with special focusing on clinical and demographic features, LBBB criteria, echocardiography (mainly LVEF) and coronary angiography (with special focusing on site, severity and number of coronary vessels affected). Results: LBBB was attributed to CAD in 57.2% of LBBB patients. Patients with LBBB and CAD were older, more in males, with increased previous MI and PCI. Also, there are a significant decrease of EF when comparing group I with group II (p<0.05). Notching of upstroke of S wave in V3 was significantly present in CAD group. Multivariate logistic regression analysis among patients with LBBB performed to find the predictors of CAD showed that EF <50% was the most significant predictor of CAD after controlling for other factors [odds ratio 0.282, 95% confidence interval (CI 0.080-0.991)] . Conclusions: Coronary angiography is usually required for definitive diagnosis of coronary artery disease in patients with LBBB. Involvement of left anterior descending (LAD) coronary artery was most common followed by left circumflex artery (LCX), followed by right coronary artery (RCA). Low LVEF is the single most significant predictor of CAD among patients with LBBB. So, those patients with LBBB and reduced EF need aggressive evaluation and treatment .