Coronal view of the interatrial and interventricular septum showing fatty infiltration of the atrial septum. Note the higher insertion of the mitral valve compared to the tricuspid valve into the fibrous skeleton of the heart. In this specimen the lipomatous hypertrophy forms a "mass" in the cephalad portion of the interatrial septum. This is clearly different from the more common type of adipose tissue infiltration in the interatrial septum. For comparison, the normal interatrial septum is shown here.