Double-chambered left ventricle is a rare congenital heart defect. The clinical features, diagnosis, treatment and patient prognosis of this lesion have not been sufficiently elaborated. The present systematic review found that the accessory ventricular septum was often an abnormal muscle band, and sometimes a membranous structure, a fibromuscular ridge, or prominent trabeculations. Less than one-third of the patients are associated with other congenital heart defects. Diagnosis of double-chambered left ventricle can usually be made by transthoracic echocardiography; however, it might be misdiagnosed as atrial or ventricular septal defect. The accessory chamber was often smaller than the main chamber, and often has wall thinning. The accessory chamber wall dysfunction/hypokinesis was seen in half of the cases. One-third patients had left ventricular outflow tract obstruction. The adult patients showed abnormal electrocardiographic findings more than in pediatrics. Nevertheless, no differences were found between adult and pediatric patients in terms of left ventricular function and structure, treatment of choice, and patient outcomes. Most patients are asymptomatic with no left ventricular obstruction, and thus do not need surgical treatment. Surgical resection of the accessory ventricular septum is warranted when the patients become symptomatic as a result of left ventricular obstruction, or associated with other congenital heart defects. The patients' outcomes are promising. Differential diagnosis should be made from other types of left ventricular outpouching, other congenital heart defects, and left ventricular non-compaction.