What Is Atrial Fibrillation?

"So my heartbeat is irregular — what does that actually mean, and should I be worried?" If a doctor has just used the words atrial fibrillation (often shortened to AFib), those are usually the first two questions. This short walkthrough answers them in order, and the video above — "What is Atrial Fibrillation," a plain-English explainer of just under a minute and a half — makes a good starting point: it describes AFib as the most common heart rhythm abnormality, one that becomes more common as we get older.

What is actually happening in the heart?

A steady heartbeat starts with an electrical signal that sweeps through the heart in an orderly way, so the two upper chambers (the atria) squeeze first and the larger lower chambers follow. In atrial fibrillation that order breaks down in the upper chambers. Instead of contracting in one coordinated beat, the atria quiver — fibrillate — in a fast, chaotic way. The lower chambers still pump, but the signal reaching them is irregular, so your pulse feels uneven: a flutter, a run of quick beats, then a pause. A companion video on this site, "Atrial Fibrillation Effects," shows what that loss of rhythm does to the heart's pumping.

What does it feel like — and can you have it without knowing?

Plenty of people notice palpitations — a racing, pounding or flip-flopping feeling in the chest. Others describe breathlessness on effort that used to be easy, unusual tiredness, light-headedness, or a vague chest discomfort. Just as often, though, AFib turns up by accident: a routine pulse check feels irregular, or a tracing is taken for another reason. Episodes can also come and go, lasting minutes or hours and stopping on their own, which is one reason it can hide for a long time.

Why do doctors take a quivering rhythm seriously?

Two reasons. First, when the atria quiver instead of squeezing, blood can slow down and pool inside them, and pooled blood is more likely to form a clot. If a clot travels to the brain, it can cause a stroke — which is why stroke prevention sits at the centre of AFib care. Second, a heart that races at an uncontrolled rate for weeks or months can tire and weaken. Neither outcome is inevitable, and both are exactly what treatment aims to head off.

How is it confirmed?

The key test is an ECG — a painless tracing of the heart's electrical activity, which shows the irregular pattern directly; our guide to what an ECG is and what it shows explains how to read one. If your episodes come and go, a normal ECG on a quiet day doesn't settle it, so you may be asked to wear a small monitor for a day or longer to catch an episode in the act. Blood tests and a heart ultrasound scan are often added to look for triggers or underlying causes, such as thyroid problems or strain on the heart.

What does treatment try to do?

Treatment has three broad aims, and your own plan may involve one or all of them. The first is to slow a racing heart back to a comfortable rate. The second, for some people, is to restore and keep a normal rhythm — sometimes with a controlled electrical reset (cardioversion) or a catheter procedure (ablation). The third is lowering clot risk: many people with AFib are offered a blood-thinning medicine, a decision your doctor bases on your individual stroke risk weighed against bleeding risk. What you should not do is start, stop or swap any of these medicines on your own — if your heartbeat suddenly races with chest pain, severe breathlessness or fainting, treat that as an emergency and seek urgent care.

MedicalVideos.com has published trusted medical videos since 2007. The site was founded by Dr. Mohamed Ibrahim, MD, PhD — physician and researcher.

Educational only — this article is general information about atrial fibrillation, not medical advice and not a diagnosis. If you are concerned about your heart rhythm, discuss it with your own doctor.

Frequently Asked Questions

What is atrial fibrillation in simple terms?
It is an irregular heart rhythm in which the heart's upper chambers quiver instead of beating in a coordinated way, so the pulse becomes uneven and sometimes fast.

Can you have atrial fibrillation without symptoms?
Yes. Some people feel nothing at all, and the condition is found when a pulse check or ECG is done for another reason. Feeling fine does not rule it out.

Why does atrial fibrillation raise stroke risk?
Because blood can pool in the quivering upper chambers and form a clot, which may then travel to the brain. Preventing that is a central part of treatment.

How is atrial fibrillation diagnosed?
An ECG recording during an episode confirms it. If episodes come and go, doctors may use a wearable monitor worn for a day or longer, plus blood tests or a heart scan to look for causes.