Double-chambered left ventricle (DCLV) is an extremely rare congenital heart disease. In this condition, the left ventricle (LV) is divided into the main left ventricular chamber (MLVC) and the accessory chamber (AC) by a septum or muscle fiber with abnormal proliferation. The MLVC and AC chambers are connected to each other and can be classified into different types on the basis of their positions. Many researchers have different opinions regarding this disease. 1 | C A S E PRE S ENTATI ONA boy was diagnosed with DCLV at our hospital. The pathological type, diagnostic points, and therapeutic schemes of this condition were considered in the context of current and relevant local and international studies and reports on DCLV. The 9-year-old boy was admitted with the major complaint of 8 years of cardiac murmur, which was originally diagnosed through physical examination when the boy was 9 months old, and 5 years of palpitations and shortness of breath. Echocardiographic examination showed that the boy has congenital heart disease and an atrial septal defect (ASD) with a length of 4 mm. The patient is always being followed up because of his slight ASD. Over the past 5 years, the patient has often experienced palpitations and shortness of breath when participating in strenuous activities. The patient's uncomfortable symptoms intensified 10 days before hospital admission.Admission examination revealed that the boy had a blood pressure of 100/62 mm Hg and heart rate of 74 times/min. The patient also exhibited nonpalpable tremors, slightly enlarged heart borders, regular cardiac rhythm, loud heart sound, and murmur in the left 3-4 sternum during the systolic period (II/III level).Coarse breathing sounds were heard in both lungs. Cyanosis and precordium abnormal uplift were not observed. The boy's liver, spleen, and subcostal areas were intangible, and his lower limbs were not edemic. The results of 12-lead electrocardiogram (ECG) and Holter monitoring obtained through aided examination indicated sinus arrhythmia with left axis deviation (Figure 1). Chest X-ray revealed an abnormal cardiac shape, as well as the localized protrusion of the left anterior margin of the heart (Figure 2).Echocardiography taken along the left ventricular long axis with an apical four-chamber view showed that the left chamber was obliquely separated into left and right chambers by abnormal muscle bundles. In the parasternal long-axis view, the size of the MLVC was 4.2 × 3.9 cm and that of the AC was 2.1 × 1.8 cm. A wide access hole with the diameter of 1.9 cm during the systolic period was found between the MLVC and AC. The flow rate from the How to cite this article: Zhang W-M, Chang D-Q, Huang J-J, et al. Double-chambered left ventricle: A rare case in a child.