The left atrium reaches 39mm, which generally refers to the end-diastolic transverse diameter of the atria, and whether it is serious or not should be combined with the size of the other atria and the structure of the heart to make a comprehensive judgment. The left atrium should not exceed 35mm, 39mm suggests that the left atrium is enlarged, if the size of the other chambers of the heart is normal, most of them belong to the enlargement of the atrium caused by aging or high blood pressure, and may also be caused by arrhythmia, which is not particularly serious in general, and should be actively controlled by blood pressure and corrected for cardiac arrhythmia. However, if it is combined with ventricular enlargement or right atrial enlargement, it may be due to valvular disease, dilated cardiomyopathy, and congenital heart disease such as atrial septal defect. In the case of atrial septal defects, for example, the structure of the heart can be restored to normal through surgery if it is not combined with pulmonary hypertension. However, if it is combined with pulmonary hypertension, it is more serious, and dilated cardiomyopathy is usually incurable. Patients with an enlarged left atrium should identify the cause of their condition and talk to their doctor if they have symptoms.