Eleven patients with left bundle branch block and chest pain suggestive of coronary arterial disease were analyzed using thallium-201 exercise scintigraphy, M-mode echocardiography and coronary arteriography. The coronary arteries were shown to be normal in all patients. A reversible anteroseptal defect on thallium-201 scintigraphy and an asynchronous septal motion on echocardiography were evident in eight patients. Thus, symptomatic patients with left bundle branch block may have reversible anteroseptal defects on thallium-201 scintigraphy which do not indicate coronary artery disease. Rather, they may be due to functional ischemia secondary to abnormal septal motion.