Atrial Fibrillation: Symptoms That Should Not Be Ignored

Published: 9 October 2026 · Next review due: 9 October 2027

Atrial fibrillation (AF) is the most common sustained heart-rhythm disorder in the UK, yet many people live with its symptoms for months before seeking an assessment. An irregular or rapid heartbeat, unexplained breathlessness, and persistent fatigue can each have several possible causes — not all of them cardiac. Understanding what the signs of atrial fibrillation may feel like, and knowing when those symptoms deserve proper clinical attention, is an important step towards protecting your long-term heart health.

Quick Answer: Atrial fibrillation symptoms commonly include an irregular or fluttering heartbeat, breathlessness, dizziness, and unusual tiredness. These symptoms can have several possible causes and are not exclusive to AF. A clinical assessment — including an ECG — is usually needed to identify whether an abnormal heart rhythm is present. If you experience sudden chest pain, severe breathlessness or collapse, call 999 immediately.

Symptoms that may warrant assessment include:

• A fluttering, racing or irregular heartbeat (palpitations)
• Breathlessness at rest or during ordinary activity
• Unexplained fatigue or reduced exercise tolerance
• Dizziness or light-headedness
• Occasional chest discomfort or a feeling of tightness
• Near-fainting or feeling faint

Symptoms alone cannot confirm or exclude atrial fibrillation. A formal cardiovascular assessment is required.

What Is Atrial Fibrillation?

Atrial fibrillation is a condition in which the upper chambers of the heart (the atria) beat chaotically and out of coordination with the lower chambers (the ventricles). Instead of a regular, rhythmic pulse, the heart produces a fast and disorganised electrical signal, which results in an irregular and often rapid heart rate.

In the UK, AF affects an estimated 1.4 million people, according to the British Heart Foundation, and prevalence increases significantly with age. It can occur without any underlying cause (known as lone AF) or alongside conditions such as high blood pressure, heart valve disease, thyroid disorders, or coronary artery disease. Alcohol consumption, obesity, and obstructive sleep apnoea are also recognised risk factors.

AF is important to identify not only because of the symptoms it causes, but because it is associated with a significantly increased risk of stroke. When the atria do not beat effectively, blood can pool and clot within them. If a clot travels to the brain, it can cause a stroke. This is why assessment and, where appropriate, anticoagulation therapy are central to AF management.

Further information about how atrial fibrillation affects the heart's electrical rhythm and how it is assessed is available from Cardiologist London.

What Are the Most Common Symptoms of AF?

Can an Irregular Heartbeat Always Be Felt?

Not always. One of the challenges with atrial fibrillation is that some people experience clear and disruptive symptoms, while others have no noticeable symptoms at all — a pattern sometimes described as “silent AF.” For those who do notice symptoms, the experience can vary considerably between individuals.

Palpitations are perhaps the most commonly reported symptom. These may be described as a fluttering in the chest, a racing or pounding heartbeat, or a sensation that the heart is “skipping” beats or beating irregularly. Some people find this unsettling even when it causes no physical limitation; others notice it only during exercise or when lying quietly in bed.

Breathlessness is another frequently reported symptom, particularly during physical activity. When the heart is beating inefficiently, the cardiovascular system is less able to meet the body's demand for oxygen. As a result, tasks that were previously manageable may begin to feel noticeably more effortful.

Fatigue and reduced exercise tolerance are common but easily attributed to other causes, such as poor sleep, stress or deconditioning. In AF, chronic fatigue may reflect the heart's reduced pumping efficiency over time.

Dizziness or light-headedness can occur when the heart rate is irregular or unusually rapid, reducing the volume of blood pumped with each beat. Dizziness linked to an underlying heart-rhythm problem can present as near-fainting episodes (pre-syncope) or, in more severe cases, actual loss of consciousness (syncope).

Chest discomfort may occasionally accompany AF, though this symptom warrants careful evaluation since it can also arise from other cardiac or non-cardiac conditions.

When Should You Seek Medical Assessment?

If you have noticed a persistent or recurring irregular heartbeat — even if it does not feel severe — it is worth discussing with a healthcare professional. The same applies if you are experiencing unexplained breathlessness, fatigue that has no obvious explanation, or episodes of dizziness that are new or worsening.

An assessment is particularly important if:

• Symptoms are recurring or becoming more frequent
• You have risk factors for AF such as high blood pressure, diabetes, obesity or a history of heart disease
• You are over 65 years of age and have not had a recent heart-rhythm check
• A family member has been diagnosed with AF or another heart-rhythm condition
• You have experienced a transient ischaemic attack (TIA) or stroke

You do not need to wait until symptoms become severe to seek an opinion. Early identification of AF allows treatment decisions — including the consideration of stroke-prevention therapy — to be made promptly.

Information about when heart palpitations warrant a specialist cardiology assessment is available from Cardiologist London.

What Tests Might Be Used to Investigate AF?

Electrocardiogram (ECG)

A standard resting 12-lead ECG remains the primary tool for detecting AF. When AF is present during the recording, the ECG will typically show an absence of organised P waves and an irregularly irregular ventricular response. However, if AF is paroxysmal (occurring in episodes rather than continuously), it may not be captured during a short resting recording.

Ambulatory Heart-Rhythm Monitoring

When symptoms are intermittent, a longer recording period is often more informative. Ambulatory ECG monitoring — sometimes called a Holter monitor — allows the heart rhythm to be recorded continuously over 24 hours, 48 hours or longer. For less frequent episodes, extended monitoring devices (worn for days or weeks) or implantable loop recorders may be considered.

Echocardiogram

An echocardiogram uses ultrasound to produce detailed images of the heart's structure and function. In the context of AF, it can help identify underlying structural conditions such as valve disease, enlarged chambers or impaired ventricular function that may have contributed to the development of arrhythmia.

Blood Tests

Thyroid function tests are routinely performed when AF is diagnosed, as an overactive thyroid (hyperthyroidism) is a recognised and treatable cause of atrial fibrillation. A full blood count, electrolytes and other markers may also be assessed.

Additional Investigations

Depending on the clinical picture, further tests such as a stress ECG, cardiac MRI or CT coronary angiography may occasionally be considered. The selection of investigations is determined by individual symptoms, clinical history and examination findings. Not every patient will require all tests.

A detailed explanation of how ambulatory ECG monitoring captures intermittent irregular heart rhythms is published by Cardiologist London.

What Might Treatment or Management Involve?

Management of AF is guided by several factors: the type of AF (paroxysmal, persistent or permanent), the severity of symptoms, the underlying cause, and the individual's risk profile for stroke and other complications.

Treatment approaches are generally discussed under two broad headings:

Rate control aims to slow the heart rate to a range that is more comfortable and efficient, without necessarily restoring a fully regular rhythm. Beta-blockers, calcium channel blockers, and digoxin are among the medications used for this purpose.

Rhythm control involves strategies aimed at restoring and maintaining a normal heart rhythm. This may include medication (antiarrhythmic drugs), electrical cardioversion (a controlled electrical shock delivered under sedation to reset the heart rhythm), or catheter ablation — a procedure in which the abnormal electrical pathways driving AF are selectively treated.

Stroke prevention is central to AF management. Anticoagulation therapy significantly reduces the risk of stroke in people with AF who meet certain clinical criteria. This is assessed using a validated scoring tool (the CHA2DS2-VASc score) that weighs relevant risk factors.

All treatment decisions should be made in discussion with a clinician responsible for your care. Do not start, stop or adjust prescribed medication without clinical advice.

Supporting Long-Term Heart Health

Alongside any prescribed treatment, evidence-based lifestyle measures play a meaningful role in managing AF and supporting overall cardiovascular health.

• Blood pressure management: Hypertension is among the most significant modifiable risk factors for AF. Regular monitoring and appropriate treatment matter.
• Alcohol: Alcohol is a well-recognised trigger for AF episodes in some individuals. Reducing consumption may lower episode frequency.
• Weight management: Obesity is associated with a higher AF burden. Sustained weight loss has been shown in clinical studies to reduce AF recurrence.
• Physical activity: Regular moderate exercise supports cardiovascular health. Discuss the appropriate level with the clinician responsible for your care.
• Sleep: Obstructive sleep apnoea is strongly linked to AF. If you experience significant snoring, witnessed apnoeas or excessive daytime sleepiness, this warrants evaluation.
• Smoking: Smoking is a significant cardiovascular risk factor. Support for smoking cessation is available through the NHS.

These measures support general heart health and do not replace clinical treatment for AF.

When to Seek Emergency Help

Call 999 immediately if you or someone nearby experiences any of the following:

• Sudden chest pain or pressure that does not settle
• Pain spreading to the arm, jaw, neck, back or stomach
• Chest discomfort accompanied by sweating, nausea or breathlessness
• Sudden severe breathlessness
• Collapse or loss of consciousness
• Sudden facial weakness or drooping
• Weakness or numbness down one side of the body
• Sudden difficulty speaking or understanding speech
• Sudden severe headache with no obvious cause

These may be signs of a heart attack, stroke or another life-threatening emergency. Do not call a clinic or wait for a routine appointment. Call 999 immediately.

For symptoms that concern you but are not an emergency, contact your GP or call NHS 111.

Frequently Asked Questions

Can AF come and go?
Yes. Paroxysmal AF occurs in episodes that start and stop on their own, sometimes lasting minutes and sometimes hours or days. Because episodes are intermittent, they may not be captured on a short resting ECG, which is why ambulatory monitoring is often used for investigation.

Is atrial fibrillation life-threatening?
AF itself is not immediately life-threatening in most cases, but it is associated with an increased risk of stroke and, over time, can contribute to heart failure if left untreated. Early identification and appropriate management significantly reduce these risks.

What does an irregular heartbeat feel like?
People describe it in various ways — a fluttering or quivering sensation in the chest, a rapid or pounding heartbeat, a feeling that the heart is racing unevenly, or the sense that beats are being skipped. The experience varies between individuals, and some people feel very little at all.

Can stress or anxiety cause similar symptoms?
Anxiety and stress can cause palpitations, chest discomfort and breathlessness that feel similar to those associated with AF. A clinical assessment, including an ECG, is necessary to distinguish between these causes. Neither AF nor anxiety should be assumed without proper evaluation.

Does a normal ECG rule out AF?
A normal resting ECG does not exclude AF, particularly if the condition is paroxysmal. Longer monitoring periods may be needed to capture an intermittent arrhythmia. The most appropriate investigation depends on individual symptoms and clinical history.

Is AF more common in older people?
Prevalence does increase with age — AF affects roughly 10% of people aged 75 and over in the UK, according to the British Heart Foundation. However, AF can also occur in younger people, particularly in the presence of certain risk factors or underlying conditions.

Further Cardiology Information

Cardiologist London publishes educational information about a range of cardiovascular conditions, symptoms and specialist investigations. The site covers topics including atrial fibrillation, palpitations, breathlessness and heart-rhythm monitoring, and is associated with the practice of Dr Ravi Assomull, a consultant cardiologist.

If you have concerns about your heart rhythm or cardiovascular health, speaking with your GP is a good first step. Your GP can arrange initial investigations and, if appropriate, refer you for specialist assessment.

This article provides general information and does not constitute individual medical advice, diagnosis or treatment. Cardiovascular symptoms can have several possible causes and should be assessed according to individual circumstances. Seek advice from an appropriate healthcare professional if symptoms persist or worsen. Call 999 immediately if you may be experiencing a heart attack, stroke or another medical emergency.