One great view to visualize the atrioventricular valve (s) is in subcostal short-axis view. The atrioventricular valve(s) are not called mitral or tricuspid. They are usually on the same plane (usually the tricuspid valve is lower than the mitral from the Cranial to caudal plane).
Type A: Most common type in Down syndrome (Trisomy 21). The superior bridging leaflets are inserted on to the LV by chordal attachments.
Type B: Least common. The superior bridging leaflets attach to the RV by chordal insertion.
Type C: Associated with Transposition of great arteries and Tetralogy of Fallot. The superior bridging leaflets have no chordal insertions and are free-floating.
To learn more on atrio-ventricular canal - click here.