Figure 2. The pushing force of flow Left: Early systolic ejection flow relative to the mitral valve in the apical 5 chamber view. In obstructive HCM the mitral leaflet coaptation point is closer to the septum than normal. The protruding leaflets extend into the edge of the flowstream and are swept by the pushing force of flow towards the septum. Flow pushes the underside of the leaflets (arrow). Note that the midseptal bulge redirects flow so that it comes from a relatively lateral and posterior direction; on the 5 chamber view, flow comes from “right field” or “one o’clock” direction. This contributes to the high angle of attack relative to the protruding leaflets. Also note that the posterior leaflet is shielded and separated from outflow tract flow by the cowl of the anterior leaflet. Venturi flow in the outflow tract cannot be lifting the posterior leaflet because there is little or no area of this leaflet exposed to outflow tract flow. Venturi forces cannot be causing the anterior motion of the posterior leaflet. MV=mitral valve, OT=outflow tract, SB=septal bulge. Right: Two apical 5 chamber echocardiographic views of one patient with obstructive HCM are shown; resting gradient = 54 mm Hg. Top: 2-D shows the protruding mitral leaflet on the first frame in systole that showed mitral coaptation. Arrowhead points to mitral valve. MV=mitral valve, OT=outflow tract, SB=septal bulge. On the next sequential frame there was fully developed SAM. Bottom: shows the same view, of the first systolic frame with color flow. Color flow is seen lateral to the leaflet tips (arrow). Color flow velocity is quite low. On the next frame there was aliased high velocity flow. These images show the event graphically drawn in left panel. Early in systole flow pushes the underside of the mitral leaflets and pushes them into the septum.