Foramen secundum
![Blood, shown in the red arrow, travels through the foramen ovale and the foramen secundum. HH: right ventricle, VH: left ventricle, HF: right atrium, VF: left atrium, LV: pulmonary vein](/Images/godic/202501/31/Foramen_ovale0223.png")
The foramen secundum, or ostium secundum, is a foramen (opening) in the septum primum, a precursor to the interatrial septum of the embryological heart.
It should not be confused with the foramen ovale, which is a foramen in the septum secundum.