Barlow's syndrome is a type of congenital heart disease affecting the Mitral valves. The presence of the symptom results in a midsystolic click, first interpreted as a mitral valve abnormality by J. B. Barlow. A congenital disorder is a medical condition or defect that is present at or before birth (for example, congenital heart disease). ... The mitral valve (also known as the bicuspid valve or left atrioventricular valve), is a dual flap (bi = 2) valve in the heart that lies between the left atrium (LA) and the left ventricle (LV). ...