Dear student,
The valve between the left atrium and left ventricle is called the bicuspid valve. This valve has only two flaps which give it the name bicuspid, these flaps look like a headdress.
It allows the blood to flow from the left atrium into the left ventricle. It is on the left side of the heart.
Bicuspid valve closes during the contraction of left ventricle (ventricular systole). If the bicuspid valve does not function properly, backflow of blood from left ventricle will take place.
Regards