patent foramen ovale
Before birth the foramen ovale is a normal flap-like opening between the two atria that lets blood bypass the unused lungs. After birth, rising left-sided pressure normally presses the flap shut, like a one-way door swinging closed and sealing over. In a patent foramen ovale, the flap never fully seals, leaving a small potential gap.
This is extremely common, present in roughly a quarter of adults, and in most people it causes no symptoms at all. The flap usually stays pressed closed, but during moments that briefly raise right-sided pressure, such as a strong cough or strain, a little blood, or a stray clot, can slip from the right atrium to the left.
Because of that occasional right-to-left passage, a patent foramen ovale is sometimes implicated when a younger person has an otherwise unexplained stroke from a clot that crossed over. In selected such cases the opening can be closed with a catheter-delivered device, but for the vast majority of people it is a harmless incidental finding.
After a young patient has a stroke with no obvious cause, a bubble study reveals a patent foramen ovale, prompting discussion of device closure.
A bubble study can reveal right-to-left passage through a patent foramen ovale.
A patent foramen ovale is not the same as an atrial septal defect: the foramen ovale is a normal structure that simply failed to seal, whereas an atrial septal defect is missing septal tissue and usually shunts left to right.