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By Does Your Duck Quack

Atrial fibrillation and blood thinners: what to know

Atrial fibrillation can raise stroke risk. Learn about checks, anticoagulants, bleeding signs and the questions to ask your healthcare team.

Checked: 13 October 2026 · Next review: 13 April 2027 · Applies to: UK, with nation notes
How this guide was prepared

Purpose: urgent guidance · Level: detailed

Checked by: Does Your Duck Quack. Sources are linked below; seek professional advice for individual circumstances.

The short answer

What to do first

Atrial fibrillation can raise stroke risk. Learn about checks, anticoagulants, bleeding signs and the questions to ask your healthcare team.

Start here: Some people notice palpitations, a fluttering or pounding heartbeat, breathlessness, tiredness, dizziness or reduced exercise tolerance. Others have no obvious symptoms and AF is found during a pulse check or another appointment. Symptoms can come and go, so write down what happened, how long it lasted, what you were doing and whether you felt faint or unwell. A symptom diary helps a clinician understand the pattern, but it does not diagnose AF. If symptoms are new or worsening, contact your GP or the relevant urgent service.

Do not wait: Call 999 for stroke signs, chest pain, collapse, or serious bleeding.

Visual guides

See the decision at a glance

AF: checks and stroke prevention
  1. 1. Notice the patternNote palpitations, breathlessness, tiredness or dizziness, including when they began.
  2. 2. Ask about testsA pulse check and ECG can help confirm an irregular rhythm.
  3. 3. Discuss preventionAsk how anticoagulants may lower clot and stroke risk in your circumstances.
  4. 4. Share the informationTell clinicians, dentists and pharmacists about anticoagulant treatment.
When to get emergency help
  1. Call 999For stroke signs, chest pain, collapse or serious bleeding.
  2. Contact your care teamFor new symptoms, questions about a missed dose or a planned procedure.
  3. After a fallSeek urgent advice after a head knock and say you take an anticoagulant.

Scope of this guide

This guide helps you understand the options and questions to ask. It is not personal medical, legal or financial advice. Check the official sources for your nation and seek qualified help for high-stakes decisions.

If someone may be in immediate danger

Call 999 for a life-threatening emergency. For an urgent problem that is not clearly life-threatening, use the official NHS urgent-care route for the UK nation you are in. Have the address, symptoms, onset time, medicines and allergies ready.

Who this guide is for

Adults newly told they may have AF, and family supporters helping prepare questions while keeping the person in control.

Atrial fibrillation (AF) is a heart rhythm problem. It can be unsettling to hear about, especially when anticoagulant treatment is discussed. This guide explains what AF may feel like, how clinicians investigate it, and how to make day-to-day conversations safer. It cannot decide whether a particular treatment is right for you: that decision depends on your health, preferences and clinical assessment.

What to do now

1. Notice symptoms, but do not rely on them

Some people notice palpitations, a fluttering or pounding heartbeat, breathlessness, tiredness, dizziness or reduced exercise tolerance. Others have no obvious symptoms and AF is found during a pulse check or another appointment. Symptoms can come and go, so write down what happened, how long it lasted, what you were doing and whether you felt faint or unwell. A symptom diary helps a clinician understand the pattern, but it does not diagnose AF. If symptoms are new or worsening, contact your GP or the relevant urgent service.

2. Ask how the diagnosis was checked

A clinician may feel your pulse and arrange an electrocardiogram (ECG), which records the heart’s electrical activity. If the rhythm is intermittent, a short ECG may not capture it, so a longer period of monitoring may be discussed. Ask what the result showed, whether the rhythm was confirmed, and what follow-up is planned. Tell the team about other health conditions, previous strokes, falls, bleeding, fainting and all medicines or supplements. These details help clinicians consider both the chance of a clot and possible bleeding concerns.

3. Understand why anticoagulants may be offered

AF can allow blood to pool in the heart and form a clot that may travel to the brain. An anticoagulant reduces clotting and can lower stroke risk, but it also makes bleeding more likely. Ask the clinician to explain your individual benefits and risks in plain language, what signs need urgent attention, and how often your treatment should be reviewed. Do not start, stop or alter prescribed treatment yourself. If prescribed medicine is missed, a new medicine is prescribed, or a procedure is planned, speak to your GP, pharmacist or specialist team for advice specific to your plan.

4. Know which bleeding changes need attention

Tell your healthcare team promptly about bleeding that is unusual for you, bruises that appear without an obvious cause, repeated nosebleeds, blood in urine or stools, or a fall involving a head knock. Seek urgent help for heavy bleeding, vomiting or coughing blood, black tarry stools, severe headache after a fall, collapse or becoming very unwell. Carry information that you take an anticoagulant and mention it before dental work, surgery or a new prescription. A clinician or pharmacist can explain what to do in your circumstances; do not wait for a routine appointment if bleeding is severe.

5. Make everyday care safer without giving up activity

Falls matter because a head injury can be more serious when someone takes an anticoagulant. Review balance, footwear, lighting and medicines with a GP or pharmacist, and tell them about any fall even if you feel well. This does not mean avoiding all movement: ask what activity is suitable and how to reduce avoidable hazards. Keep a current medicines list and share it with anyone treating you. Before a procedure or a medicine change, make sure the responsible clinician knows about AF and your anticoagulant.

6. Know when symptoms are an emergency

Use FAST for possible stroke: face weakness, arm weakness, speech difficulty and time to call 999. Do not wait to see if these signs pass. Chest pain, collapse, severe breathlessness or serious bleeding also need emergency help. If the person cannot explain what is wrong, note when they were last well and what has changed. Keep emergency contacts and medicine information somewhere responders can find them. For non-emergency questions, write them down for the GP, nurse, pharmacist or anticoagulation service and ask who to contact outside normal hours.

7. Plan procedures and check other treatments

Tell the team arranging an operation or invasive test that you take an anticoagulant, even if the procedure seems unrelated to your heart. Include dental treatment in that conversation. The clinician responsible for the procedure and the team managing your anticoagulant need to agree any changes; do not stop treatment simply because a booking letter mentions bleeding. Before buying another medicine, herbal remedy or supplement, check with the pharmacist or anticoagulation team. Some treatments can change the effect of an anticoagulant, including medicines bought without a prescription. Check the leaflet supplied with your medicine for other possible side effects and discuss persistent troublesome symptoms with the GP or anticoagulant clinic.

Warning signs and checks

Common questions

Can you have atrial fibrillation without symptoms?

Yes. Some people feel palpitations, breathlessness, tiredness or dizziness, while others notice nothing. AF may be found when a clinician checks an irregular pulse or investigates another concern. Feeling well does not confirm that AF has gone away, and symptoms alone cannot identify the rhythm. If you have a new concern, ask your GP how it should be assessed.

Why might I be offered a blood thinner for AF?

AF can increase the chance of a clot forming in the heart and travelling to the brain. Anticoagulants reduce clotting and can lower stroke risk, while also increasing bleeding risk. A clinician weighs these issues using your individual health history and preferences. Ask for the likely benefits, risks, monitoring and warning signs in language you understand; do not make changes without professional advice.

What should I do if I fall while taking an anticoagulant?

If you hit your head, feel faint, are injured or become unwell, seek urgent medical advice and tell the clinician that you take an anticoagulant. Call 999 for severe symptoms, collapse or serious bleeding. Even when there is no obvious injury, let your GP or care team know about falls so they can review balance, medicines and your safety plan.

When should I call 999 for possible AF-related symptoms?

Call 999 for signs of stroke, including sudden face or arm weakness or speech difficulty, even if they improve. Chest pain, collapse, severe breathlessness and serious bleeding also require emergency help. Do not drive yourself. For milder new or recurring symptoms, contact your GP or the urgent advice route recommended by your NHS team.

Do I need to tell my dentist about a blood thinner?

Yes. Tell the dentist that you take an anticoagulant before treatment, especially if an extraction is being considered. The NHS says you may not need to stop your medicine, although a blood test may be needed before the procedure. Only stop treatment on advice from your GP or another healthcare professional. Ask who will explain the plan and whether the dental team needs information from your anticoagulation service. Keep that advice with your appointment details so everyone is working from the same instructions.

Differences across the UK

AF assessment and prescribing are NHS services across the UK, but local pathways and specialist follow-up can differ. In England, Scotland, Wales and Northern Ireland, start with the GP or urgent service advised by your care team. Ask which service manages your monitoring and who to contact outside normal hours.

When to get urgent help

Call 999 for stroke signs, chest pain, collapse, or serious bleeding.

Primary sources

The publisher checked this guide against the 6 official sources below. This is an editorial source check, not approval by a clinician, lawyer or benefits adviser.

Editorial note: By Does Your Duck Quack.