Mild mitral regurgitation may cause mild enlargement of the atria. 1. Mitral valve insufficiency causes the left ventricle to contract, part of the blood is ejected to the whole body through the aorta, and part of it will regurgitate to the left atrium, resulting in more blood in the left atrium, increased diastolic pressure, and compensatory enlargement of the left atrium. If the regurgitation is only mild, it may not cause the left atrium to increase in size for a short period of time. Prolonged regurgitation will lead to an increase in the size of the left atrium and the symptoms of mitral valve insufficiency will gradually become more serious over time. 2. There are many diseases leading to mitral valve insufficiency, the common clinical ones are mitral valve damage caused by rheumatic heart disease; myocardial infarction, coronary heart disease and other diseases involving the papillary muscles of the valve, leading to its dysfunction, which leads to damage of the mitral valve; left ventricular enlargement leading to the relative mitral valve closure insufficiency and so on.