摘要：The electrocardiographic(Fig. 1) has been recorded from an asymptomatic 52-year-old woman free from organic heart disease,who was admitted to the outpatient department beacause a routine ECG had pointed out some abnormalities1: ①The QRS axis is at +90°, ②The QRS duration is 0.14 seconds, ③ The QRS configuration in the limb leads is suggestive of BBB, but it is hard to define, on the basis of these leads only, which type of BBB (right or left) is involved2.The wide S waves in leads I and aVL suggest at first glance an RBBB, whereas the QRS morphology in the inferior leads (monophasic R wave with secondary ST-T changes) is more consistent with an LBBB with relative right axis deviation, ④The chest leads further complicate the problem because lead V1 suggests an RBBB, whereas leads V5 and V6 are perfectly consistent with an LBBB, showing a monophasic R wave3, in addition, lead V5 shows ST-segment depression and negative T wave, typical of LBBB. It is worth noting that when the tracing was recorded, the correct placement of precordial electrodes was accurately checked, ⑤ Placement of precordial electrodes of leads V4,V5,and V6 2 intercostals spaces above restores4,in these leads, a QRS configuration suggestive of RBBB:small and relatively wide s waves appear and the T waves become positive.