What are endocardial cushions?
Regions of dense connective tissue that form at specific cardiogenic
sites where endocardial cells undergo mesenchymal transformation
and  invade cardiac jelly.
                 Where are they located?
Form septum intermedium (separates right and left AV canals)
Participate in atrial septum(separates right and left atria)
Participate in ventricular septum (membranous portion)
Participate in aorticopulmonary septum (separates pulmonary and
   aortic outflow tracts-seeded by neural crest cells)