Patent foramen ovale (PFO) is a small channel present in the fetal heart which does not close at birth and persists after the age of 1 year.
When PFO is small, it has no clinical manifestation and remains asymptomatic. The clinical consequences begin to appear when PFO is large, especially in terms of strokes and transient ischemic events with an undefined etiology . Many affected individuals also present with migraine, but it is not known whether this condition is due to transient ischemic attacks (TIA) or to paradoxical embolism.
PFO might become very dangerous for those who practice extreme sports. For instance, neurologic decompression sickness is very common in scuba divers, who appear to be at a higher risk of nitrogen gas embolism and hypoxemia when they are at great depth. Other clinical manifestations of PFO, which are less frequent but nevertheless very dangerous and insidious, include acute myocardial infarction  , systemic and fat embolism  , and left-sided valve disease .
In the majority of cases, PFO is completely asymptomatic and have no major clinical manifestation. However, after 50 years of age individuals might begin to present with typical signs such as cryptogenic strokes, ischemia (especially TIA), pain in a limb with a sudden onset, embolism and less frequently migraine headaches. A history of congenital heart diseases and decompression illness, together with dyspnea associated with postural change and platypnea-orthodeoxia syndrome, strongly suggests the presence of PFO .
While laboratory tests are not necessary, an fundamental role in the diagnosis is played by imaging studies, particularly echocardiography . Suspected cases can be analyzed with transthoracic echo (TTE), which is the method of choice for a variety of reasons such as the more sensitive and specific detection and better visualization. Intracardiac echo, instead, is used only in the cases of percutaneous closure because of its high costs and invasive nature.
Transcranial Doppler is less frequently used than echocardiography due to the impossibility to visualize PFO defects and the higher risk of producing false positives. However, transcranial Doppler can allow to diagnose shunting through PFO  permitting higher detections of abnormal flows. MRI and CT scanning, instead, might be used to detect atrial septal defects, deep vein thrombosis or paradoxical embolism.
No treatment is necessary in the cases of asymptomatic PFO. In the cases in which PFO is associated with unexplained neurological events, antiplatelet therapy is particularly recommended, alone or in combination with warfarin to prevent stroke.
Surgical closure is performed especially in the cases of large PFOs. This procedure allows a permanent closure of the defect, which prevents the occurrence of future paradoxical emboli and avoids long-term anticoagulation and the risks associated. However, the closure requires a general anesthesia and an open-heart surgery, implying a high risk of possible complications. Surgical closure is particularly indicated in the cases presenting with PFOs more than 25 mm in diameter and inadequate rim of tissue around the defect, or in the cases of percutaneous device failure.
Percutaneous closure, instead, is becoming a new therapeutic option. The procedure requires a 24-48 hours stay in the hospital and a 6 months treatment with aspirin or warfarin after the procedure. The Federal Drug Administration (FAD) has approved two percutaneous devices, which have proved to be very effective in closing PFOs: CardioSEAL Septal Occlusion System (NMT Medical Inc, Boston, MA), in polyester fabric and with an umbrella-like shape, and Amplatzer PFO Occluder (AGA Medical Corp, Golden Valley, Minn), a self-expanding wire mesh made up of two discs. This procedure is recommended for several clinical conditions and events, such as recurrent cryptogenic stroke or coronary embolism due to presumed paradoxical embolism.
The prognosis of PFO varies according to its severity. In the cases where PFO is small and asymptomatic, the prognosis is excellent and patients do well in life without major clinical treatment. But the situation is different with larger PFOs that unfortunately might have severe clinical consequences in the individuals affected. These persons have a risk of recurrent stroke and ischemia that is 3 times higher than that in normal individuals, and when PFOs are associated with atrial septal aneurysm the risk is even 6 times higher   . After percutaneous closure the risk becomes low, but still remains substantial and not negligible  .
Having an apparently spontaneous origin, PFO is technically defined as idiopathic.
Although its origin is still unknown, PFO is very frequent, reportedly found in 10% to 15% of the patients who undergo contrast echo. In a study conducted in an autopsy series, there were 29% of the patients who had a PFO 0.2 to 0.5 cm in diameter and another 6% of them who had a PFO 0.6 to 1.0 cm in diameter . According to another study, the incidence should be around 27% usually associated with PFOs with a diameter varying from 1 to 19 mm , even though it apparently declines with age underling an automatic closing in adulthood.
While no predominance related to gender and age has ever been found, there seems to be certain racial- and ethnic-related differences in PFO incidence according to several epidemiological studies  . In any case, incidence of PFO has increased over the last decades, due to increasingly sophisticated diagnostic methods and their availability, especially among those affected by stroke and ischemia.
In the utero, the foramen ovale works as a temporary right-to-left shunt which is maintained as long as pulmonary circulation is established. After birth and with the appearance of the previously mentioned pulmonary system, the left atrial pressure begins to increase and the foramen ovale closes. The closure should be complete by the age of 1 year, with the fusion of the septum primum and septum secundum. However, in certain circumstances that still remain unknown this closure does not occur, and the foramen ovale persists even after the first year of life. The diameter of PFO is on average 3.4 mm in the first decade, but increases to an average of 5.8 mm in the following decades due to the progressive stretching of the valve of the fossa ovalis .
In the past PFO was believed to be an anomaly of secondary importance, but with the increasingly larger number of data confirming its high incidence in the normal population and its pivotal role in the pathogenesis of important pathological conditions such as paradoxical embolic events, the relative importance of PFO as pathology is now being re-evaluated. Its pathological effect can be easily understood by considering the anatomical position of PFO, which allows it to increase right atrial pressure more than the left one. This effect predisposes individuals to hemostasis and clot formation, can induce paradoxical flow and cause an embolic event. This change in the conception of PFO is now pushing physicians to alter the way of managing this clinical condition.
Improving mobility is highly recommended after clinical procedure to avoid deep vein thrombosis. Subjects known to have PFOs should avoid those activities which increase right atrial pressure, such as straining or Valsalva maneuver, to prevent events of paradoxical embolism. Treatment with aspirin or warfirin is required in the 6 months following the surgical closure, and patients should always comply with the prescription of these drugs to prevent future recurrent events.
In the fetal heart, the foramen ovale is an opening which allows blood from the right atrium to enter the left one, working as fetal cardiac shunt to bypass the pulmonary circulation. This channel normally closes at birth, but in certain individuals it does not, leaving a blood flow between the right and left atrium which might have some severe clinical consequences such as decompression sickness and paradoxical embolism. In the medical terminology the word “patent” means unobstructed, in other words, PFO is an unobstructed or still opened fetal heart channel.
PFO is particularly frequent among patients with atrial septal aneurysms linked to cryptogenic stroke  and might play an important role in the pathogenesis of some migraine headaches . It is generally classified based on its size in two major groups, small PFO with a diameter less than 10 microbubbles and large PFO with a diameter greater than 10 microbubbles.
Patent foramen ovale (PFO) is a small channel present in the heart which does not close at birth and persists after the age of 1 year. In the fetus, the foramen ovale is an opening which allows blood from the right atrium to enter the left one to bypass the circulation coming from the lungs. This channel normally closes at birth, but in certain individuals it does not, leaving a blood flow between the right and left atrium which might have some severe clinical consequences.
For the majority of the cases PFO is small and asymptomatic. The clinical consequences begin to appear when PFO is large, especially in terms of strokes and transient ischemic events with an undefined origin. Many affected individuals can also present with migraine.
Treatment options include surgical closure, closure with a percutaneous device, anticoagulant and antiplatelet agents. Improving mobility is highly recommended after clinical procedure to avoid deep vein thrombosis. Subjects known to have PFOs should avoid those activities which increase right atrial pressure, such as straining or Valsalva maneuver, to prevent events of paradoxical embolism. Treatment with anticoagulant and antiplatelet agents (eg. aspirin or warfirin) is required in the 6 months following the surgical closure, and patients should always comply with the prescription of these drugs to prevent future recurrent events.