The mitral valve ( MY-trəl), also known as the bicuspid valve or left atrioventricular valve, is one of the four heart valves. It has two cusps or flaps and lies between the left atrium and the left ventricle of the heart. The heart valves are all one-way valves allowing blood flow in just one direction. The mitral valve and the tricuspid valve are known as the atrioventricular valves because they lie between the atria and the ventricles. In normal conditions, blood flows through an open mitral valve during diastole with contraction of the left atrium, and the mitral valve closes during systole with contraction of the left ventricle. The valve opens and closes because of pressure differences, opening when there is greater pressure in the left atrium than ventricle and closing when there is greater pressure in the left ventricle than atrium. In abnormal conditions, blood may flow backward through the valve (mitral regurgitation) or the mitral valve may be narrowed (mitral stenosis). Rheumatic heart disease often affects the mitral valve; the valve may also prolapse with age and be affected by infective endocarditis. The name of the mitral valve is derived from the word mitre, referencing the ceremonial headdress worn by Roman Catholic bishops, due to the resemblance between the two leaflets of the valve and the distinctive shape of the headdress.

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