Any disease that can cause an increase in the volume of the left atrium can cause enlargement of the left atrium, such as hereditary diseases or acquired adverse factors, mainly long-term smoking, diabetes mellitus, hyperlipidemia, hypertension, rheumatic heart disease, cardiomyopathy, mitral stenosis, aortic stenosis, and cardiac infarction. Thus any disease that can cause an increase in the volume of the left atrium may result in the elongation of myocardial fibers, causing structural enlargement and hypertrophy of the left atrium. The most common causes of enlarged right atrium are pulmonary heart disease, congenital heart disease, pulmonary embolism, and right ventricular infarction.