What is the difference between a patent foramen ovale and atrial septum defect?

Different. Patent foramen ovale is a temporary natural opening between two atria that allows fetal circulation to occur. Once born it closes spontaneously. An atrial septal defect is an abnormal opening between two atria that occurs due to incomplete formation of the atrial wall. It does not close spontaneously usually and may need surgery if it causes significant flow issues.

Related Questions

Please help! What is the difference between patent foramen ovale and atrial septum defect?

Similar. An ostium secundum atrial septal defect and a patent foramen ovale are both "holes" in the same place in the atrial septum, which is the wall between the right and left atria. Everyone has a different definition. In infancy, many will call a hole less than 3 or 4 mm in diameter a pfo as they almost all go on to close without treatment. Some call all defects with flow from la to RA an asd. Read more...

How is an emboli able to traverse a patent foramen ovale if the net flow of blood is from left to right atrium?

Paradox. This does seem to be a paradox but while the net flow is in the opposite direction there is some flow from right to left. If the clot is near there at just the right time it goes troug. Read more...
Possible. The heart is a pump and a dynamic process. The net pressure is from high to low. But invariably with activity motion and changing in position the flow can switch transiently. If a clot is in the flow at that time then it can become an arterial emboli with all its consequences. Read more...