An antiarrhythmic (heart-rhythm medicine)
Flecainide
A medicine that restores and maintains a normal heart rhythm in atrial fibrillation and some other arrhythmias — used only in people without significant structural heart disease.
What is Flecainide?
Flecainide treats abnormal fast heart rhythms, particularly atrial fibrillation and some other supraventricular arrhythmias, by helping the heart return to and stay in its normal rhythm. It is used only in people whose heart is structurally normal (no significant heart-muscle damage or coronary disease), because in a damaged heart it can be dangerous. Some people use it as a "pill-in-the-pocket" to stop an occasional attack.
Education and reference only. This is a plain-language guide to Flecainide — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Flecainide is an antiarrhythmic medicine used to restore and maintain a normal heart rhythm in atrial fibrillation and certain other fast rhythms that arise above the heart’s main pumping chambers. It is one of the more effective "rhythm-control" drugs, but it is used specifically in people whose heart is otherwise structurally normal. For some people with infrequent attacks, it is used as a single "pill-in-the-pocket" dose to stop an episode. It is taken as a tablet, and sometimes given by injection in hospital.
How it works
Flecainide slows the movement of electrical signals through the heart by blocking sodium channels that heart cells use to fire. This stabilises the heart’s electrical activity and interrupts the abnormal circuits that cause fast rhythms such as atrial fibrillation, helping the heart return to, and stay in, its normal rhythm. Because it slows electrical conduction, it can be harmful in a heart already scarred by a previous heart attack or weakened by heart failure — which is why a healthy heart structure is required.
What it treats
Conditions Flecainide is used for
Practical use
How to take Flecainide
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it exactly as prescribed; the amount and any "pill-in-the-pocket" use are set individually.
- If you use it "pill-in-the-pocket", follow the specific instructions on when to take it and when to seek help.
- Do not stop suddenly without advice; changes are made with your cardiology team.
- Attend ECG checks so the effect on your heart’s electrical activity can be monitored.
- Report fainting, new or different palpitations, or worsening breathlessness.
Weighing it up
Advantages & disadvantages of Flecainide
Advantages
- Effective at restoring and maintaining normal rhythm in atrial fibrillation and related arrhythmias.
- Can be used as an occasional "pill-in-the-pocket" for infrequent attacks in suitable people.
- Well established, with tablet and injection forms.
Disadvantages
- Only safe in people without significant structural heart disease.
- Can, uncommonly, provoke dangerous rhythms — needs ECG monitoring and often a rate-control partner drug.
- Interacts with some medicines and is affected by kidney function.
Practical use
Good to know
Flecainide is effective but must be used in the right person: it is only for people without significant structural heart disease (no previous heart attack, significant coronary artery disease or heart failure), because in a damaged heart it can trigger dangerous rhythms. It is often combined with a rate-controlling medicine (such as a beta-blocker) in atrial fibrillation to prevent an uncommon situation where the rhythm speeds up. Heart tracings (ECGs) are used to check it is working safely. If prescribed as a "pill-in-the-pocket", you will be told exactly when and how to use it. Report fainting, palpitations that feel different, or breathlessness.
Who should not take it / use with caution
- People with a previous heart attack, significant coronary artery disease, heart failure, or certain conduction problems.
- People with certain other structural heart abnormalities or specific arrhythmias.
- Used with care in significant kidney or liver impairment; considered individually in pregnancy.
Monitoring
- ECG (to confirm safe effect on conduction)
- Kidney function and potassium
- Heart rhythm and symptoms
Side effects
- Common: dizziness, visual disturbances (blurring), and mild nausea, especially early on.
- Important: it can occasionally provoke new or worsened abnormal rhythms (pro-arrhythmia) — hence ECG monitoring.
- Sometimes tiredness, tremor or, rarely, effects on mood or the blood count.
Key interactions
- Amiodarone raises flecainide levels — the flecainide amount is usually reduced.
- Other heart-rate-slowing or rhythm drugs (beta-blockers, verapamil, diltiazem) add to effects on the heart.
- Some antidepressants and other medicines affect its level; care with medicines that alter potassium.
Available as: Tablets; also an injection used in hospital.
Answers
Flecainide: frequently asked questions
Why can only some people take flecainide?
Flecainide is reserved for people whose heart is structurally normal — no previous heart attack, significant coronary artery disease or heart failure — because in a damaged or scarred heart it can trigger dangerous rhythms. Your cardiologist checks your heart with tests before prescribing it to make sure it is safe for you.
What is "pill-in-the-pocket"?
For some people with infrequent atrial-fibrillation attacks and an otherwise healthy heart, flecainide can be taken as a single dose only when an attack occurs, to restore normal rhythm — rather than every day. This is set up carefully by a specialist, usually after checking the approach works safely under supervision first, with clear instructions on when to use it and when to seek help.
Why am I also on a beta-blocker with it?
In atrial fibrillation, flecainide is often paired with a rate-controlling medicine such as a beta-blocker. This guards against an uncommon situation where the rhythm converts to a rapid regular one (atrial flutter) that could otherwise speed the heart up. The two work together for safe rhythm control.
Do I need heart tracings on flecainide?
Yes — ECGs are used to check that flecainide is affecting your heart’s electrical activity within a safe range, especially when starting or changing the dose. This is part of using it safely, alongside checks of your kidney function and potassium.
Authoritative sources
- BNF: Flecainide acetate.
- electronic Medicines Compendium (SmPC): Flecainide (Tambocor).
- NICE NG196: Atrial fibrillation – diagnosis and management.
Building a medicines information resource?
We create evidence-led, dose-free drug and formulary references for teams.