Also, these clefts are often more twisting and have one or two tight junctions and zona adherens interacting with a circumferential actin filament band and several connecting proteins7. These tight junctions localize to the luminal side of the intercellular clefts, where the glycocalyx, which is important in cell–cell recognition and cell signaling, is more developed. The organization of the endocardial endothelium and the intercellular cleft help to establish the blood-heart barrier by ensuring an active transendothelial physicochemical gradient of various ions1.