Anterolateral muscle bundle of the left ventricle, bulboventricular flange and subaortic stenosis.

A hitherto unrecognized muscle bundle in the left ventricular outflow tract is described. Found between the left coronary aortic semilunar cusp and the anterior leaflet of the mitral valve, this anterolateral muscle bundle of the left ventricle is present in approximately 40 percent of normal hearts. On embryologic grounds it is suggested that this bundle is a muscular remnant of the left extremity of the bulboatrioventircular flange. It can be very prominent, causing obstruction of both the left ventricular inflow and outflow tracts.