New forms of ventricular pacing are increasingly studied as an option in the management of patients with heart failure. Coronary artery disease (CAD) is the most frequent cause of heart failure, and patients with complete left or right bundle branch block (LBBB and RBBB) and a reduced left ventricular ejection fraction (LVEF) are the best candidates for this new therapy. However, the prevalence of this clinical presentation is uncertain. During a 1-year period, 433 patients with documented CAD (mean age 64 +/- 10 years, 79% men) who were referred for myocardial perfusion imaging were prospectively studied. All patients underwent a 2-day stress-rest gated 99mTc-Tetrofosmin SPECT study with evaluation of resting LV enddiastolic (LVEDV) and endsystolic (LVESV) volumes and LVEF. The resting ECG was examined in all patients for the presence of complete LBBB or RBBB. Of the 433 patients with CAD 36 patients (8.3%) had LBBB (n = 14) or RBBB (n = 22) and a QRS width > 120 ms. These 36 patients were in general older and more frequently had diabetes and atrial fibrillation. Patients with LBBB or RBBB had a significantly lower LVEF (41 +/- 16% vs 48 +/- 14%, P < 0.01) and significantly higher LV volumes compared to patients without LBBB or RBBB (177 +/- 79 mL vs 131 +/- 53 mL, P < 0.001 for LVEDV and 116 +/- 76 mL vs 73 +/- 49 mL, P < 0.001 for LVESV). In total, 112/433 (26%) had an LVEF < or = 40%; 16 had also a LBBB or RBBB (3.7% of the whole population, 14% of the patients with a LVEF < or = 40%). Within the group of patients with a LVEF > or = 40%, patients with BBB had comparable LVEF (26 +/- 9% vs 30 +/- 8%, P = NS) but significantly higher LVEDV and LVESV (230 +/- 70 mL vs 190 +/- 64 mL, P < 0.05 for LVEDV and 170 +/- 65 mL vs 135 +/- 56 mL, P < 0.05 for LVESV). In this prospective registry 3.7% of all patients with known CAD had LBBB or RBBB in combination with a LVEF < or = 40%. This represented 14% of all patients with a LVEF > or = 40%. These limited numbers should be kept in mind when considering biventricular pacing as a new therapeutic options in patients with heart failure.