Background and Aim: It remains unknown how and where the mitral valve leaks in functional mitral regurgitation. The objective of the current study was to quantify the geometry and position of the leaflet free edges in order to reveal gapping mechanism of the mitral valve, and develop a plug technique to prevent mitral regurgitation. Methods: Eight porcine mitral valves were sutured onto a dilated annulus in an in-vitro experiment to simulate valve closure at hydrostatic transmitral pressure. Eight sonocrystals were attached to the mitral valve leaflet free edges. Papillary muscles (PM) were adjusted to the normal position, and subsequently to positions of asymmetric and symmetric papillary muscle displacement. Sonocrystal positions were measured and analyzed. Results: The leaflet free edges in the central and medial regions moved medially, apically, and posteriorly from normal to asymmetric PM position. Gapping potential in the posteromedial region increased. Medial displacement of the free edges sometimes generated a gap in the anterolateral region in the asymmetric PM position. The leaflet free edges moved posteriorly and apically from the normal to symmetric PM position, and generated a dumb-bell shaped gap. Conclusions: Asymmetric PM position impairs the posteromedial coaptation region due to leaflet tenting, and compromises the anterolateral coaptation region due to medial leaflet displacement. The gaps include multiple sites along the coaptation line. Symmetric PM position impairs valve coaptation due to valve tenting only. The gap is a symmetrical dumb-bell shape. The findings are crucial for development of the plug technique to prevent mitral regurgitation.