A cardiac ultrasound LA43mm refers to an internal diameter of the left atrium of 43mm. During cardiac ultrasound, the size of the left atrium is indicated by the left atrial internal diameter, or LA, which has a normal range of 25 to 35 mm, and if it is greater than 40 mm, left atrial enlargement can be diagnosed. Clinically, the main diseases that lead to left atrial enlargement are mitral stenosis, mitral valve insufficiency, hypertension and restrictive cardiomyopathy. 1. Mitral stenosis: At this time, the resistance to blood outflow from the left atrium increases, and the amount of blood accumulated in the left atrium increases, and in the long run, the amount of blood in the left atrium is getting more and more, which causes the expansion of the left atrium. 2. Mitral valve insufficiency: During the contraction of the left ventricle, the blood flows back to the left atrium through the insufficiently closed mitral valve, which also leads to an increase in the left atrial blood, and finally causes dilatation of the left atrium due to its failure to compensate. 3. Hypertension: causes an increase in the afterload of the left ventricle, and long-term hypertension leads to compensatory hypertrophy of the left ventricle, which leads to an increase in the resistance of the left atrial blood to enter the left ventricle, and the left atrium is dilated in a compensatory manner. 4. Restrictive cardiomyopathy: This leads to stiffness of the ventricular wall and reduced diastolic capacity, and increased resistance of left atrial blood to enter the left ventricle. If the left atrium is found to be enlarged, further examination should be carried out to clarify the cause of the disease and then treat the symptoms, so as to avoid delaying the disease.