ovale) shut, therefore closing the foramen ovale as well. In normal development, the closed foramen ovale fuses with the interatrial wall. During the first breath, vasoconstriction causes the ductus arteriosus to close, and during adult years, tissue occludes what once was the ductus arterious, creating the ligamentum arteriosum. Clinical significance Aneurysm Aneurysms can occur in adulthood if the foramen ovale is not closed correctly. An aneurysm happens when an artery becomes enlarged in a localized area due to weakening of the arterial wall. When this type of aneurysm occurs in the area of the fossa ovalis, an enlarged pouch is formed. This pouch can protrude into the right atrium or the left atrium. The cause of this aneurysm is the result of abnormal, increased pressure within the heart. Even if the foramen ovale does seal shut, an aneurysm may occur, usually on the side of the right atrium. If the aneurysm stretches too far, it can narrow the opening of the inferior vena cava. This type of aneurysm can be a result of plaque build-up in the arteries from coronary heart disease, as well as diseases of the aortic valve or mitral valve. Surgery may be useful in helping to cope with the aneurysm. Patent foramen ovale If the atrial septum does not close properly, it leads to a patent foramen ovale (PFO). This type of defect generally works like a flap valve, opening during certain conditions of increased pressure in the chest, such as during strain while having a bowel movement, cough, or sneeze. With enough pressure, blood may travel from the right atrium to the left. If there is a clot in the right side of the heart, it can cross the PFO, enter the left atrium, and travel out of the heart and to the brain, causing a stroke. If the clot travels into a coronary artery it can cause a heart attack. See also Fetal circulation References External links – "Right atrium, internal structure, anterior view" Diagram Dissection photo Cardiology