part of endocardium development GO:0003157 The process whose specific outcome is the progression of the endocardium over time, from its formation to the mature structure. The endocardium is an anatomical structure comprised of an endothelium and an extracellular matrix that forms the innermost layer of tissue of the heart, and lines the heart chambers. biological_process 2009-10-01T12:42:27Z dph heart development anatomical structure development