Top: Line drawing of outflow relative to the mitral valve in early systole. Note the anterior position of the mitral valve coaptation. The prominent mid-septal bulge redirects outflow so that it comes from a relatively posterior direction, catching the anteriorly positioned mitral valve and pushing it into the septum.
Second: After subaortic septal resection. The subaortic septum has been resected, but only down to the tips of the mitral leaflets. Flow is still redirected by the remaining septal bulge so that it comes from a posterior direction. It still catches the mitral valve; SAM persists, as does obstruction.
Third: The septal bulge below the mitral leaflet tips has been resected, an extended myectomy. Now, flow tracks more anteriorly and medially, away from the mitral leaflets.
Bottom: Mobilization and partial excision of the papillary muscles is added to extended myectomy. The mitral coaptation plane is now more posterior, explicitly out of the flow stream.