Background <p>Left bundle branch block (LBBB) mainly occurs in those with heart disease, but also appears in asymptomatic patients with normal heart structure. Determining the causal relationship between LBBB and cardiomyopathy is a current clinical challenge.</p> Case presentation <p>This article describes a case of a middle-aged female patient with complete LBBB and cardiac dysfunction whose symptoms significantly improved after cardiac resynchronization therapy (CRT). During follow-up assessments at 3 and 6&#xa0;months postsurgery, echocardiography revealed good recovery of cardiac structure and function, with a significant improvement in cardiac functional classification (NYHA). A comparison of the preoperative and postoperative echocardiographic data revealed that the patient's cardiac structural and functional indicators improved. The patient was ultimately diagnosed with LBBB-induced dilated cardiomyopathy (LIC). Additionally, the potential value of cardiac magnetic resonance (CMR) imaging for predicting the therapeutic effect of CRT on LIC was demonstrated.</p> Conclusion <p>Through the analysis of medical history, cardiac ultrasound, and CMR imaging, LIC can be detected early and accurately.</p>