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Figure 6 Flow strikes the undersurface and lateral aspect of the mitral valve very early in systole, causing SAM. Two echocardiographic views of one patient with obstructive HCM are shown; resting gradient = 54 mm Hg. (Left) Apical five-chamber view. (Top left) The 2-D image shows the protruding mitral leaflet on the first frame in systole that showed mitral coaptation. Arrowhead points to mitral valve. O indicates outflow tract. (Bottom left) The same view showing the first systolic frame with color flow. Color flow is seen lateral to the leaflet tips (arrow). These images show the event graphically drawn in Figure 4. (Right) Apical three-chamber view. (Top right) The 2-D image again shows the protruding mitral leaflet on the first frame in systole that showed mitral coaptation. Arrowhead points to mitral valve. (Bottom right) This shows the same view of the first systolic frame with color flow. Color flow is seen posterior to the leaflet tip (arrow). Note that color flow velocity is low on both views. On 2-D imaging, the next systolic frames showed fully developed SAM on both views. On color flow, the next systolic frames showed aliasing in the outflow tract. The mitral leaflets are medially and anteriorly positioned into the edge of the flow stream. Low velocity flow strikes the undersurface of valve leaflets; they are swept toward the septum by the pushing force of flow.