Here’s a transesophageal echo (TEE) of a subaortic membrane (encircled in yellow) causing left ventricular outflow tract (LVOT) obstruction. Also note the fluttering of the aortic valve (AoV) leaflets during systole, turbulent flow in the LVOT, and chordal systolic anterior motion (SAM) of the mitral valve (MV). Surgeons will resect this membrane to alleviate the outflow obstruction and improve overall forward systemic flow.
Most subaortic membranes I’ve encountered are just below the level of the aortic valve, but this example is much more proximal in the LVOT.