Patent foramen ovale (PFO) is a flaplike opening between the atrial septa primum and secundum at the location of the fossa ovalis (see the image below) that persists after age 1 year. With increasing evidence being found that PFO is the culprit in paradoxical embolic events, the relative importance of the anomaly is being reevaluated.
Signs and symptoms
Most patients with isolated PFO are asymptomatic. When they do occur, signs and symptoms can include the following:
History of stroke or transient ischemic event of undefined etiology
Migraine or migraine-like symptoms - Whether symptoms are due to transient ischemic attacks or paradoxical embolism is not clear
Neurologic decompression sickness - Seen with PFO in a small percent of scuba divers
Other, less common clinical manifestations of PFO include the following:
Systemic embolism, such as renal infarction 
Fat embolism 
Paradoxical embolism caused by right atrial tumors that increase right atrial pressure 
Left-sided valve disease in carcinoid syndrome 
See Clinical Presentation for more detail.
The following types of echocardiography can be used in the detection of PFO:
Color flow Doppler imaging - A small "flame" of color signal may be seen in the middle region of the atrial septum
Contrast echocardiography - Usually required to detect a small PFO
Two-dimensional transesophageal echocardiography (2-D TEE) with contrast - Provides superior visualization of the atrial septum
Three-dimensional transesophageal echocardiography (3-D TEE) - Provides direct visualization of the entire PFO anatomy and surrounding structures 
Transmitral Doppler (TMD) echocardiography - In current practice, the role of TMD is uncertain due to limited experience with this modality 
Transcranial Doppler (TCD) - An alternative to TEE; however, although it can detect a right-to-left shunt, it cannot show the shunt’s location 
See Workup for more detail.
Most patients with a patent foramen ovale (PFO) as an isolated finding receive no special treatment. No consensus exists on the treatment of PFO in patients with transient ischemic attack or stroke.
When PFO is associated with an otherwise unexplained neurologic event,  traditional treatment has been antiplatelet (ie, aspirin) therapy alone in low-risk patients or such therapy combined with the use of warfarin in high-risk individuals, to prevent cryptogenic stroke.
Surgical closure of PFO with double continuous suture has resulted in elimination of residual shunt across the PFO.
Indications for surgical closure include the following:
PFO of more than 25 mm in size
Inadequate rim of tissue around the defect
Percutaneous device failure
Percutaneous closure of PFO during cardiac catheterization is another, less-invasive therapeutic option. Indications for its use include the following:
Recurrent cryptogenic stroke due to presumed paradoxical embolism (resulting from PFO failure of conventional drug therapy)
Contraindications to anticoagulant treatment
Alternative to medical therapy or surgical closure - Cryptogenic transient ischemic attack due to presumed paradoxical embolism through a PFO
Presumed paradoxical peripheral or coronary embolism through a PFO
Cryptogenic stroke, transient ischemic attack, or peripheral or coronary embolism due to presumed paradoxical embolism (through a PFO that is associated with a hypercoagulability state)
Patent foramen ovale (PFO) is an anatomical interatrial communication with potential for right-to-left shunt. Foramen ovale has been known since the time of Galen. In 1564, Leonardi Botali, an Italian surgeon, was the first to describe the presence of foramen ovale at birth. However, the function of foramen ovale in utero was not known at that time. In 1877, Cohnheim described paradoxical embolism in relation to PFO.
See also the Medscape Drugs & Disease articles Atrial Septal Defect and Pediatric Atrial Septal Defects.
Patent foramen ovale (PFO) is a flaplike opening between the atrial septa primum and secundum at the location of the fossa ovalis that persists after age 1 year. In utero, the foramen ovale serves as a physiologic conduit for right-to-left shunting. Once the pulmonary circulation is established after birth, left atrial pressure increases, allowing functional closure of the foramen ovale. This is followed by anatomical closure of the septum primum and septum secundum by the age of 1 year.
The Mayo Clinic autopsy study revealed that the size of a PFO increases from a mean of 3.4 mm in the first decade to 5.8 mm in the 10th decade of life, as the valve of fossa ovalis stretches with age. 
With increasing evidence that PFO is the culprit in paradoxical embolic events, the relative importance of the anomaly is being reevaluated. James Lock, MD, postulated that PFO anatomy results in a cul-de-sac between the septa primum and secundum, predisposing individuals to hemostasis and clot formation. Any conditions that increase right atrial pressure more than left atrial pressure can induce paradoxical flow and may result in an embolic event.
This reasoning has greatly altered the previous conception of PFO and is changing current management of the condition.
United States statistics
Patent foramen ovale (PFO) is detected in 10-15% of the population by contrast transthoracic echocardiography. Autopsy studies show a 27% prevalence of probe-patent foramen ovale.  This difference is probably due to the ability to directly visualize PFO on autopsy study, while contrast echocardiography relies on detection of secondary physiologic phenomena.
Sex- and age-related demographics
The prevalence and size of probe-patent PFO is similar in males and females.
The prevalence of PFO declines progressively with age—34% up to age 30 years, 25% for age 30-80 years, and 20% older than 80 years.