Objective:To evaluate the value of surface electrocardiogram clues for the differential diagnosis of idiopathic left ventricular tachycardia and wide QRS complex supraventricular tachycardia. Methods:Surface ECGs and clinical data of 75 patients with wide QRS complex tachycardia of right bundle branch block type and without organic heart disease were analyzed retrospectively, and the final diagnoses were made by intracardiac electrophysiological study. Results:The valuable surface ECG clues for the diagnosis of idiopathic left ventricular tachycardia were as follows:(1) evidence of atrioventricular dissociation, (2)evidence of capture or fusion beats, (3)axis of “no man’s land”(-90°~180°) or left axis deviation, (4)negative direction S wave is predominating in inferior wall leads(Ⅱ-Ⅲ and avF),(5)QRS morphology in lead Ⅰ was characterized biphasic Rs wave; QRS morphology in lead avL was Rs or qR or qRs;QRS morphology in lead V6 was characterized biphasic rS wave;(6)it occurs transient reversible T change during sinus rhythm after tachycardia termination. And the valuable surface ECG clues for the diagnosis of superventricular tachycardia with wide QRS complex were as follows: (1)normal axis or right axis deviation, (2)positive direction R wave is predominating in inferior wall leads(Ⅱ-Ⅲ and avF); QRS morphology in lead avL was biphasic rS or QS;(3)QRS morphology in lead V6 was characterized biphasic Rs wave. Conclusion:Surface ECG clues are valuable for differential diagnosis of wide QRS complex tachycardia of right bundle branch block type and without organic heart disease. Several features are extracted in this text for differential diagnosis idiopathic left ventricular tachycardia and supraventricular tachycardia of wide QRS complex.