Background Double-chambered left ventricle (DCLV) is an extremely rare congenital disease that is often asymptomatic and undiagnosed until adulthood. The incidence of double-chambered right ventricle (DCRV) is estimated to be one in 36000 patients, while the incidence of DCLV is certainly even lower. To data, only a handful of cases of DCLV have been reported. Case Summary A 4-year-old boy was admitted to the local hospital in 2019 due to chest discomfort. He had mild tachypnea and wheezing. Upon physical examination, his heart was found to be enlarged without any obvious cardiac murmur. Cardiac percussion also revealed enlargement of the heart, and further echocardiography confirmed a diagnosis of ‘dual-chamber left ventricle’. No other cardiac or systemic abnormalities were observed. In January 2022, the patient came to our hospital for further diagnosis and treatment. The laboratory results including coagulation testing were no obvious abnormality. The 24-hour Holter revealed sinus rhythm with left bundle branch block (I°). The bedside chest X-ray indicated abnormal protrusion of the left margin of the heart. Transthoracic echocardiography showed that the left ventricle was divided into main and accessory chambers by a thick muscle bundle in the middle of the left ventricular cavity. Cardiac magnetic resonance (CMR) confirmed this, and additionally found a giant thrombus in the accessory cavity (AC). Discussion DCLV is an extremely rare congenital heart disease which is often asymptomatic and undiagnosed until adulthood. The etiology of DCLV is still unclear, however, some reports have suggested that it may be related to hypoplasia of the regional myocardial intra-trabecular sinusoids or an intramyocardial aneurysm during the embryonic period. Additionally, some cases have indicated that DCLV may be a subtype of genetic ardiomyopathies. DCLV is characterized by the subdivision of the left ventricle into two chambers by abnormal septum or muscle bands. This case report introduces a patient with DCLV and giant thrombus, in which cardiovascular magnetic resonance (CMR) imaging plays an important role in the diagnosis and differential diagnosis.

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