We prospectively analyzed the clinical, echocardiographic, and coronary arteriographic data of 51 patients with type 2 diabetes mellitus with left bundle branch block (LBBB), 51 patients with type 2 diabetes mellitus without LBBB, and 51 patients with isolated LBBB matched for age and gender. Extent of coronary artery disease (CAD) was classified according to the standard method into 1-, 2-, or 3-vessel disease and was estimated by calculation of the Gensini score. The left ventricular ejection fraction was analyzed by echocardiography. Age, gender, and percentage of patients with a smoking habit or family history of CAD did not differ among the groups. The rates of hypertension and levels of serum creatinine, cholesterol, and triglycerides were statistically higher in group I compared with the other 2 groups. Patients with diabetes and LBBB (group I) had significantly higher scores for the severity (Gensini score) of CAD (p < 0.001) and more 3-vessel disease (p < 0.001). After adjustment for hypertension, hypertriglyceridemia, and hypercholesterolemia with covariance analysis, the presence of LBBB was also associated with a higher Gensini score in patients with diabetes compared with those with diabetes but without LBBB and those with isolated LBBB (p < 0.001). The present study, for the first time, has shown that patients with type 2 diabetes mellitus and concomitant LBBB have more severe and extensive CAD and advanced left ventricular dysfunction compared with those with diabetes but without LBBB and those with isolated LBBB. (c) 2006 Elsevier Inc. All rights reserved.