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Health condition

PFO, or patent foramen ovale - explained simply.

PFO is short for patent foramen ovale, a common and usually harmless small opening in the heart. This quick guide covers the essentials - for full detail on symptoms, diagnosis and treatment, see our complete patent foramen ovale guide.

Read the full PFO guide
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Why trust this guide

  • 01

    Editorial team

    Written by our editorial team from the UK sources listed on each page.

  • 02

    Sourced from guidance

    Checked against ESC, RCP and peer-reviewed sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK guidance on cryptogenic stroke workup and percutaneous PFO closure.

Key facts

PFO at a glance.

The essentials, in plain English. For the full clinical picture, read our complete patent foramen ovale guide.

  • What PFO stands for

    Patent foramen ovale - a small flap-like opening between the right and left atria that failed to seal fully after birth.

  • How common it is

    Present in around 1 in 4 adults - most people with a PFO have no symptoms and never need treatment.

  • Why it matters

    A PFO can allow a clot to cross from the venous side to the arterial side - paradoxical embolism - a recognised cause of cryptogenic stroke.

  • Diving risk

    A PFO raises the risk of decompression illness in divers by letting nitrogen bubbles bypass the lungs.

  • How it is confirmed

    Bubble-study echocardiography - a contrast echo that shows bubbles crossing from right to left.

  • Main options

    From no treatment at all through to a percutaneous closure device, chosen on a case-by-case basis for cryptogenic stroke.

When it matters

Mostly silent, occasionally significant.

A PFO rarely causes problems on its own. These are the situations where it becomes clinically relevant.

  • Usually silent

    Most people with a PFO have no symptoms at all - it is often found by chance during scans for something else.

  • Cryptogenic stroke

    A stroke or TIA with no clear cause found on standard workup is the main trigger for PFO testing in younger adults.

  • Diving decompression illness

    Unexplained decompression illness after a dive within accepted limits can point to a right-to-left shunt.

  • Migraine with aura

    An association exists with migraine with aura, though closure is not routinely offered for migraine alone.

  • Often an incidental finding

    Found unexpectedly on an echocardiogram performed for an unrelated reason - reassurance is usually all that is needed.

Want the full picture on how bubble-study echocardiography works and how the cryptogenic stroke workup is done? Our complete patent foramen ovale guide covers diagnosis step by step.

Treatment

From reassurance to closure.

Management ranges from doing nothing at all to a percutaneous closure device for carefully selected cryptogenic stroke patients.

  • Reassurance and no treatment

    The right choice for most people - an incidental PFO with no stroke history carries very low risk.

  • Antiplatelet therapy

    Low-dose aspirin may be used in selected cases where closure is not indicated or not yet decided.

  • Percutaneous closure device

    A catheter-delivered device seals the defect - considered for selected patients under 60 with a cryptogenic stroke and high-risk PFO features.

  • Diving advice

    Divers with a confirmed PFO are counselled on conservative diving profiles or closure if diving is important to them.

What this guide is based on

The sources behind every claim on this page.

UK and European national guidance, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP or cardiologist knows your history and can tell you which parts apply to you. If in doubt, get seen.

  • European Society of Cardiology (ESC). Guidelines on the management of patent foramen ovale.

  • Royal College of Physicians (RCP). National Clinical Guideline for Stroke.

  • NICE. Percutaneous closure of patent foramen ovale for secondary prevention of recurrent stroke.

  • British Heart Foundation. Patient information on PFO.

Red flags

When to seek urgent care.

A PFO itself is rarely an emergency. These related situations are.

  • New stroke or TIA symptoms

    Sudden facial droop, arm weakness or slurred speech is a medical emergency - call 999 immediately, whatever the PFO history.

  • Decompression illness after diving

    Joint pain, breathlessness or confusion after a dive needs urgent assessment at a hyperbaric or emergency unit.

  • Recurrent stroke on treatment

    A further event despite antiplatelet therapy warrants prompt specialist re-review of the closure decision.

  • New breathlessness after closure

    Rare but reportable - device-related arrhythmia or erosion needs same-day cardiology assessment.

Living with it

A common finding, rarely a problem.

For most people, discovering a PFO changes very little. These four points cover what matters day to day.

A quiet reminder

Having a PFO is not the same as having heart disease.

It is a variant of normal anatomy in roughly a quarter of adults - context is everything.

  1. 01 Context

    Most PFOs need nothing

    An incidental PFO with no stroke or diving history is not a disease - it does not usually change how you live.

  2. 02 Workup

    Get the full stroke picture

    Closure decisions rest on a full cryptogenic stroke workup, not the PFO finding alone.

  3. 03 Diving

    Tell your dive medic

    Anyone who dives regularly and has a known PFO should discuss it with a dive medicine specialist.

  4. 04 Decide

    A shared decision

    Closure versus medical therapy is a shared decision between you and a stroke and cardiology team, weighing age and PFO features.

Frequently asked

Everything we get asked about PFO.

Quick answers on what PFO stands for, diagnosis, stroke risk and closure. For more depth, see our full patent foramen ovale guide.

  • What does PFO stand for?

    PFO stands for patent foramen ovale - a small, flap-like opening between the right and left upper chambers (atria) of the heart that everyone has before birth and which normally seals shortly afterwards.

  • Is a patent foramen ovale (PFO) dangerous?

    For most people, no. Around a quarter of adults have one and never know it. It becomes clinically relevant mainly when it is linked to a cryptogenic stroke, unexplained decompression illness in divers, or in some migraine-with-aura patients.

  • How is PFO diagnosed?

    The standard test is bubble-study (contrast) echocardiography - agitated saline is injected into a vein and, on echo, bubbles crossing early from the right side of the heart to the left confirm a shunt.

  • Does a PFO cause stroke?

    It can, via paradoxical embolism - a small clot travels from a vein, crosses the PFO, and lodges in a brain artery. This is one recognised cause of cryptogenic stroke, particularly in younger adults with no other risk factors found.

  • When is PFO closure recommended?

    Closure with a percutaneous device is considered for selected patients, usually under 60, who have had a cryptogenic stroke and high-risk PFO features on imaging, decided jointly by stroke and cardiology specialists.

  • Can I still dive with a PFO?

    Many people do, but a confirmed PFO raises the risk of decompression illness. Discuss conservative diving profiles, or whether closure makes sense, with a dive medicine specialist.

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