本文选取3例临床诊断明确、同时描记有常规心电图及心电向量图的左束支阻滞患者，其中2例真性左束支阻滞患者的心电向量图起始向量均位于左前，向前向量减小，20 ms向量位于左后，呈8字形运行，环体中部及终末部运行缓慢；1例左心室肥厚伴分支型完全性左束支阻滞（假性左束支阻滞）患者，心电向量图起始向量位于右前，20 ms向量仍位于左前，QRS环最大向量振幅明显增大。结合患者临床病史综合分析，发现心电向量图对真性左束支阻滞有很高的诊断价值，并能解释真性左束支阻滞的心电图附加诊断标准。

This paper takes three patients definitely diagnosed with left bundle branch block(LBBB) for case study. Their   routine electrocardiogram(ECG) and vectorcardiogram(VCG) were synchronously recorded. On the VCGs of two patients with true LBBB, the starting vector was oriented in the leftfront side with forward vector reduced; 20ms vector was oriented in the leftrear side  operating in the form of an 8character shape; the central and terminal parts of the ring operated slowly. In one patient with left ventricular hypertrophy complicating branchtype complete LBBB(false LBBB), the starting vector was oriented in the rightfront side, 20ms vector was still leftfront oriented, and the amplitude of the maximal vector of QRS loop significantly increased. Combined with the patients clinical medical histories, VCG was found highly valuable in  diagnosing true LBBB and made explanation of the additional ECG diagnostic criteria of true LBBB become possible.