--- title: Patent foramen ovale description: What a patent foramen ovale is, how it differs from an atrial septal defect, why it is linked to stroke of unknown cause, how it is found, when it is closed and when to call an ambulance. type: disease aliases: - PFO - open foramen ovale sources: - tier: guideline org: minzdrav-rf title: Ишемический инсульт и транзиторная ишемическая атака year: 2024 url: https://cr.minzdrav.gov.ru/view-cr/814_1 - tier: guideline org: minzdrav-rf title: Дефект межпредсердной перегородки year: 2023 doi: 10.15829/1560-4071-2023-5588 url: https://cr.minzdrav.gov.ru/view-cr/46_2 - tier: guideline org: nice title: Percutaneous closure of patent foramen ovale to prevent recurrent cerebral embolic events (HTG325) year: 2013 url: https://www.nice.org.uk/guidance/htg325 - tier: review title: 'Embolic strokes of undetermined source: a clinical consensus statement of the ESC Council on Stroke, the European Association of Cardiovascular Imaging and the European Heart Rhythm Association of the ESC' year: 2024 doi: 10.1093/eurheartj/ehae150 url: https://doi.org/10.1093/eurheartj/ehae150 - tier: review title: European position paper on the management of patients with patent foramen ovale. General approach and left circulation thromboembolism year: 2019 doi: 10.1093/eurheartj/ehy649 url: https://doi.org/10.1093/eurheartj/ehy649 - tier: review title: 'European position paper on the management of patients with patent foramen ovale. Part II: Decompression sickness, migraine, arterial deoxygenation syndromes and select high-risk clinical conditions' year: 2021 doi: 10.4244/EIJ-D-20-00785 url: https://doi.org/10.4244/EIJ-D-20-00785 - tier: reference org: msd-manuals title: Overview of Congenital Cardiovascular Anomalies (MSD Manual Professional Version) year: 2025 url: https://www.msdmanuals.com/professional/pediatrics/congenital-cardiovascular-anomalies/overview-of-congenital-cardiovascular-anomalies - tier: reference org: msd-manuals title: Perinatal Physiology (MSD Manual Professional Version) year: 2025 url: https://www.msdmanuals.com/professional/pediatrics/perinatal-physiology/perinatal-physiology - tier: reference org: msd-manuals title: Ischemic Stroke (MSD Manual Professional Version) year: 2026 url: https://www.msdmanuals.com/professional/neurologic-disorders/stroke/ischemic-stroke - tier: textbook title: Anatomy and Physiology 2e (OpenStax), 19.1 Heart Anatomy year: 2022 isbn: 9781711494067 url: https://openstax.org/books/anatomy-and-physiology-2e/pages/19-1-heart-anatomy sources_checked: 2026-10-14 review: null --- A patent foramen ovale (PFO) is a slit in the wall between the atria left over from the circulation before birth: in the unborn baby, blood passes through the foramen ovale from the right atrium into the left, bypassing the lungs, which are not yet breathing. The opening usually closes after birth, but in about 1 in 4 people it stays fully or partly open. Most people with a PFO have no problems from it. However, a blood clot from the veins can pass through it into the arteries and cause a stroke. A PFO is not the same as an [atrial septal defect](../atrial-septal-defect/): the Russian Ministry of Health guideline explicitly excludes PFO from the definition of that defect.

After birth the pressure in the right atrium falls and the pressure in the left atrium rises, and the two parts of the wall between the atria are pushed against each other; in most people they then fuse and the opening no longer exists. What remains in its place is the fossa ovalis, a remnant of the foramen ovale. More about it in the article on the [heart chambers](../../anatomy/heart-chambers/).

With a PFO the two parts of the wall have not fused. Usually they lie pressed together and let little or no blood through. On ultrasound a flap of the septum primum is seen next to the opening, and blood passes through it at a slant: this is how a PFO is told apart from a septal defect. When the pressure in the right side of the heart rises, a little blood may pass through the slit from right to left. This is why the bubble test must always include straining, and why symptoms of a stroke starting during straining in a young person may point to a clot passing through the opening.

## Why it happens Before birth the lungs do not breathe, and blood bypasses them through the foramen ovale, from the right atrium into the left. After birth the pressure in the right atrium falls and the pressure in the left atrium rises; the septum primum is pushed against the septum secundum like a flap, and the opening closes. In about three people out of four the two parts later fuse; in the rest the opening stays open. A PFO is common, so it is often a chance finding rather than the cause of an illness. The danger lies elsewhere. A clot from the veins, for example in [deep vein thrombosis](../deep-vein-thrombosis/) of the legs, can cross through the opening from the right side of the heart into the left and from there into the arteries. If it blocks an artery in the brain, the result is a stroke or a transient ischaemic attack (TIA). This is called paradoxical embolism. Before birth the foramen ovale is kept open by the difference in atrial pressures: left atrial pressure is low because little blood returns from the lungs, while right atrial pressure is high because large volumes of blood return from the placenta. Closure after birth is at first functional: the septum primum is pushed against the septum secundum. A PFO is found in about 25% of people; the position paper gives a prevalence of 20–30%. In adults, shunting through a PFO may be minimal or absent. Besides paradoxical embolism, a thrombus may form within the PFO tunnel itself; left atrial dysfunction and atrial arrhythmias are also discussed. Anything that raises pressure in the right heart chambers, such as [pulmonary hypertension](../pulmonary-hypertension/), can increase a small shunt. PFO is a frequent cause of cryptogenic stroke in younger patients, mainly through paradoxical embolism; a large PFO and an associated atrial septal aneurysm raise the risk. The Russian Ministry of Health guideline classes PFO and atrial septal aneurysm as sources of low and uncertain cardioembolic risk and names PFO as one of the possible causes of embolic stroke of undetermined source (ESUS). ESUS is a non-lacunar stroke with no obvious source of embolism after work-up and exclusion of known causes, in particular cardioembolism and atherosclerosis proximal to the stroke territory. ## Symptoms In most people a PFO causes no symptoms at all. It is often found by chance; doctors look for it in particular when searching for the cause of a stroke. If a clot has passed through the opening, signs of a stroke or TIA appear: sudden weakness of the face muscles or limbs and numbness, especially on one side of the body, and difficulty speaking. In young people, paradoxical embolism is suggested by recent immobility (a long journey, a flight, illness or an operation), venous thrombosis or [pulmonary embolism](../pulmonary-embolism/), dehydration, and symptoms that start on waking or during straining, such as lifting something heavy, coughing or sneezing. PFO has also been linked with other conditions. It is more common in people with migraine, especially migraine with aura, than in the general population. In divers, gas bubbles from the veins can cross a PFO into the arteries when right heart pressure rises; in decompression sickness without obvious risk factors the position paper advises considering a search for PFO. A shunt through a PFO can lower arterial oxygen saturation, but in most cases it only aggravates a pre-existing cause of hypoxaemia. The most common cause of the rare platypnoea–orthodeoxia syndrome is a PFO. When a PFO is found by chance in a pilot or a diver with no history of decompression sickness, conventional flights are not restricted; for recreational divers the position paper advises talking with an experienced diving physician about whether to stop diving or to undertake only low-risk dives. ## How it is diagnosed Everyone who has had an ischaemic stroke or TIA has a [heart ultrasound (echocardiography)](../../diagnostic/echocardiography/) to look for a source of clots in the heart. A shunt through a PFO is looked for with a bubble test: the ultrasound shows whether microbubbles pass from the right atrium into the left or into the arteries of the brain. The test must always include straining (the Valsalva manoeuvre). There is no need to look for a PFO "just in case": the diagnosis is needed only when it will decide treatment. It is also important to check for [atrial fibrillation](../atrial-fibrillation/): repeat embolisms are in most cases caused by clots in the left atrial appendage, not by the opening. The Russian Ministry of Health guideline recommends transcranial Doppler with a bubble test in patients aged 18–55 with ESUS to diagnose paradoxical embolism; the alternative is transthoracic echocardiography with a bubble test. A positive bubble test is an indication for transoesophageal echocardiography to confirm the source of the shunt and assess its anatomy. The Russian Ministry of Health guideline calls transoesophageal echocardiography the "gold standard" for detecting a right-to-left shunt. The position paper stresses that no technique can be considered a reliable gold standard and that a precise diagnosis usually needs a combination of techniques. In the trials, shunt size was graded on transoesophageal echocardiography by the number of microbubbles in the left atrium during the first three cardiac cycles after they appeared in the right atrium: no bubbles means no shunt, 1–5 a small shunt, 6–25 a moderate shunt and more than 25 a large shunt. A large shunt and an atrial septal aneurysm were regarded as high-risk features for embolism. The likelihood of a causal link between a PFO and a cryptogenic stroke is assessed with the RoPE score, which gives points for no history of hypertension, diabetes, stroke or TIA, for not smoking, for a cortical infarct and for younger age. The RoPE score does not account for septal aneurysm; the PASCAL classification combines it with the anatomy of the PFO. On echocardiography a secundum ASD is distinguished from a PFO: with a PFO a flap of the septum primum is seen next to the opening, and the colour Doppler flow runs at a slant. ## How it is treated In most people a PFO does no harm, and guidelines propose closing it only in particular situations. If a stroke has happened with no other cause found and the PFO has high-risk features, the Russian Ministry of Health guideline recommends closing the opening with a special device, an occluder. The device is passed through a vein in the groin to the heart and opened inside the opening under imaging guidance, such as ultrasound; the procedure is done under local anaesthesia with sedation or under general anaesthesia. After closure, antiplatelet medicines are taken for a long time; which ones and for how long is decided by the doctor. The decision to close a PFO is made together by an interventional cardiologist, other specialists depending on how the condition shows itself, and the patient. Open-heart surgery just for a PFO is rarely done; the opening may be closed along the way during another heart operation. The Russian Ministry of Health guideline recommends transcatheter device closure followed by long-term antiplatelet therapy to prevent recurrent stroke in patients aged 18–60 with ESUS, a PFO and a high risk of embolism (grade of recommendation C). Anticoagulants are not recommended for preventing recurrent stroke in this group. The benefit of closure is reduced by a low RoPE score (0–3), older age and the need for anticoagulants, and increased by a high RoPE score, younger age without conventional stroke risk factors, a history of deep vein thrombosis or prothrombotic states, previous non-lacunar or cortical strokes and failure of antiplatelet therapy. Since 2017, several trials have shown that percutaneous PFO closure reduces the risk of recurrent stroke in patients who meet ESUS criteria; this evidence comes from patients younger than 60, and trials are needed in older patients. The most frequent undesirable event after closure is atrial fibrillation; the most frequent late complication is device thrombosis; serious complications include device embolisation and atrial wall erosion, which has been reported only anecdotally. NICE advises that the procedure be done only in units with arrangements for urgent cardiac surgical support. For migraine, the position paper advises conventional migraine treatment and PFO closure not as routine, only in clinical trials or for compassionate use in migraine with aura. After decompression sickness, behaviour and diving technique are changed first; closure is discussed if that is not possible or does not work, with shared decision-making that stresses the lack of evidence. ## When to call an ambulance In most people a PFO causes no problems. The danger is a stroke, if a clot passes through the opening into an artery of the brain. Call your local emergency number (112 in the EU, 911 in the US and Canada, 999 in the UK) straight away if there is sudden weakness of the face muscles or limbs, especially on one side of the body, numbness, difficulty speaking or understanding speech, or loss of consciousness. The Russian Ministry of Health guideline describes a quick test to recognise a stroke: ask the person to smile, to speak and to raise both arms. If they have difficulty doing any of these, call an ambulance, describe the symptoms and tell the paramedics when they began. As with any heart condition, call an ambulance for fainting, chest pain or severe breathlessness: this is the site's general safety rule, repeated at the bottom of every page.