1) The valve between the left atrium and left ventricle of the heart.

2) A valve in the heart that guards the opening between the left atrium and the left ventricle, prevents the blood in the ventricle from returning to the atrium, and consists of two triangular flaps attached at their bases to the fibrous ring which surrounds the opening and connected at their margins with the ventricular walls by the chordae tendineae and papillary muscles -- called also bicuspid valve, left atrioventricular valve.