On the atrial surface of the leaflets exist two zones, one peripheral smooth or body zone and one central rough or coaptation zone, which is irregular and thicker due to the numerous chordae attached to its ventricular side. The gently curved coaptation line between the two leaflets evident from an atrial view, separates these two areas. The rough zone represents the coaptation surface of the valve.  The coaptation zone of the valve is critical to valve competency, and the depth and length of coaptation is now often viewed as an important assessment of mitral valve function.

_{* Modified from Carpentier A, Adams DH, Filsoufi F. Carpentier’s Reconstructive Valve Surgery. From Valve Analysis to Valve Reconstruction. 2010 Saunders Elsevier.}