Arrhythmogenic cardiomyopathy (ACM) is an inherited cardiac disease characterized by fibrofatty replacement of ventricular myocardium. Ventricular arrhythmia and sudden cardiac death (SCD) are the main clinical manifestations[1-3](#ref-0001). ACM was previously called arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D). However, recent studies have shown that this disease is not limited to the right ventricle; in ACM, biventricular involvement reaches 50%. Subsequently, the left-dominant subtype was also identified, which supported the adoption of the broader term “arrhythmogenic cardiomyopathy” [1-3](#ref-0001). In this report, we describe a case of secondary syncope in a patient with ACM who developed right bundle branch block with ventricular tachycardia (RBBB-VT), considering that VT originated in the left ventricle. Cardiac magnetic resonance (CMR) of the patient showed enlargement of the left atrium and left ventricle and significant thinning of most of the free wall of the left ventricle. The movement of the left ventricular wall was significantly weakened and nearly disappeared (LVEF, 30%). Late gadolinium enhancement (LGE) and fat sequencing showed that most of the left ventricular free wall was replaced by fibre and adipose tissue. Therefore, the diagnosis was considered to be arrhythmogenic left ventricular cardiomyopathy (ALVC), and CMR played a key role in the diagnosis.