English: This is a modified version of Manco Capac's Atrial Septal Defect Diagram demonstrating incomplete closure of the central foramen ovale by the septum primum. The foramen ovale is is essential for babies in utero (in the womb) and closes after delivery when the rim of septum primum tissue adheres to the main septum secundum. It is common that closure is not entirely complete and a small leak can remain under certain circumstances. This is referred to as a patent foramen ovale.