Echocardiography appears to be a sensitive technique for detecting disturbances in left ventricular posterior wall motion in subjects with WPW type A. The characteristic abnormality consists of premature anterior displacement of the LVPW shortly after the inscription of the delta wave. The ability to detect abnormal wall motion is influenced by the size of the segment of myocardium undergoing pre-excitation, the site of insertion of the anomalous pathway, and its accessibility to echocardiographic study. The results of this study support the concept that WPW type A represents premature excitation of the posterior left ventricular wall in some patients. Moreover, such pre-excitation may be associated with an altered pattern of left ventricular contraction. A similar pattern of LVPW motion was not observed in a large group of randomly selected clinical echocardiograms including a variety of intraventricular conduction disturbances.