A fixed subaortic membrane typically consists of a collar or ridge of membranous and/or fibromuscular tissue extending from the ventricular septum into the left ventricular outflow tract and resulting in subaortic stenosis. The fibromuscular ridge is often discrete, but can be circumferential with attachments to the mitral valve or diffuse and tunnel-like. This is rarely seen in the neonatal period, but rather develops and progresses over time due to an abnormal proliferation of fibrous tissue. There is an associated congenital heart defect in more than 50% of cases. Common associated defects include ventricular sepal defect, coarctation of the aorta, atrioventricular septal defect, valvular aortic stenosis and congenital anomalies of the mitral valve.