The cardiac jelly formed around the hea tube during early development, contributes to the formation of:

Prior to looping, the acellular space between the myocardium and endocardium in the hea is filled with a deformable extracellular matrix, the cardiac jelly, secreted by the myocardium. Radioactive labeling demonstrates that proteins produced in the myocardium flow toward the endocardium and are incorporated into the basal lamina. The cardiac jelly has a variety of functions related to hemodynamic performance, cardiac looping, and cell migration in cardiac septation and formation of the endocardial cushion valves at the atrioventricular (AV) junction and outflow tract of the hea. Ref: Keller B.B., Markwald R.R., Hoying J.B. (2011). Chapter 9. Molecular Development of the Hea. In V. Fuster, R.A. Walsh, R.A. Harrington (Eds), Hurst's The Hea, 13e.