Left atrioventricular orifice
The left atrioventricular orifice (left atrioventricular opening or mitral orifice) is placed below and to the left of the aortic orifice.
It is a little smaller than the corresponding aperture of the opposite side.
It is surrounded by a dense fibrous ring, covered by the lining membrane of the heart, and is guarded by the bicuspid or mitral valve.