An additional structure in the right atrium is the opening of the coronary sinus, which receives blood from most of the cardiac veins and opens medially to the opening of the inferior vena cava. Associated with these openings are small folds of tissue derived from the valve of the embryonic sinus venosus (the valve of the coronary sinus and the valve of inferior vena cava, respectively). During development, the valve of the inferior vena cava helps direct incoming oxygenated blood through the foramen ovale and into the left atrium.