What is arrhythmia? Cardiologist explains

If you have felt your heart flutter, race, pause or “skip a beat”, you may have wondered whether you have an arrhythmia. The word can sound alarming, but it covers a wide range of heart rhythms (heartbeats). Some are harmless and need only reassurance; others deserve investigation or treatment.

In simple terms, an arrhythmia is a problem with the rate (speed) and/or rhythm (nature) of the heartbeat. The heart may beat too quickly, too slowly or irregularly. The important question is not simply, “Is my pulse unusual?” but, “What rhythm is causing it, why is it happening, and does it carry any risk?”

This blog post explains the main types of arrhythmia, their symptoms and causes, how a cardiologist investigates them, and the treatments that may help.

Importantly, please call 999 if palpitations occur with chest pain, severe breathlessness, fainting, collapse, or symptoms of a stroke.

This article is general information and cannot diagnose an individual heart rhythm.

Figure 1 — Normal sinus rhythm is regular, while atrial fibrillation produces disorganised atrial activity and an irregularly irregular pulse.

What does a normal heartbeat do?

Your heart is both a pump and an electrical organ. A normal beat usually begins in the sinoatrial node, a small group of specialised cells in the right upper chamber (the right atrium). This natural pacemaker sends an electrical signal across the atria, then through the atrioventricular node and into the ventricles—the heart’s main pumping chambers.

This coordinated sequence allows the heart to fill and pump efficiently. A typical resting heart rate for an adult is often described as 60–100 beats per minute, although a healthy rate can sit outside that range. Fit people, for example, may have a resting pulse below 60 without any problem. Context and symptoms matter more than a number alone.

An arrhythmia develops when electrical signals start abnormally, follow an extra circuit, become disorganised, or travel too slowly through the heart. The result may be:

• Tachycardia: a heart rhythm that is too fast.
• Bradycardia: a heart rhythm that is too slow for the person’s needs.
• An irregular rhythm: beats occur in an uneven pattern.
• Premature or ectopic beats: an early beat interrupts the usual rhythm, often followed by a short pause.

The American Heart Association’s overview (1) similarly defines arrhythmia by abnormal speed or rhythm, while the British Heart Foundation (2) provides helpful UK patient information on rhythm disorders.

What are the most common types of arrhythmia?

“Arrhythmia” is an umbrella term rather than one diagnosis. Common examples include the following.

Ectopic beats

An ectopic beat begins earlier than expected in an atrium or ventricle. People often describe a thump, flip, missed beat or momentary pause. Ectopic beats are extremely common and are frequently benign, particularly when the heart is structurally normal. Caffeine, alcohol, stress, poor sleep and illness may make them more noticeable. Frequent ectopics, persistent symptoms or an abnormal examination may justify further assessment.

Atrial fibrillation

Atrial fibrillation (AF) is a common arrhythmia in which electrical activity in the atria becomes chaotic. The pulse is typically irregular and may be fast. Some people feel palpitations, fatigue or breathlessness; others notice nothing.

AF matters because it can allow blood to stagnate in the atria and form a clot, increasing the risk of stroke in some patients. Risk is assessed individually, and anticoagulant medication may be advised. The NHS guide to atrial fibrillation (3) and NICE guideline NG196  (4) explain the UK approach to diagnosis, stroke prevention and management. The 2024 European Society of Cardiology AF guideline (5) emphasises treatment of underlying conditions alongside stroke prevention and symptom control.

Supraventricular tachycardia

Supraventricular tachycardia (SVT) is a rapid rhythm arising above the ventricles, often because an electrical impulse repeatedly travels around a small circuit. Episodes commonly start and stop suddenly. The heartbeat may feel very fast and regular, and symptoms can include light-headedness, breathlessness or chest discomfort. SVT is often treatable, including with catheter ablation when appropriate. More details can be found on NHS SVT overview (6) and the ESC clinical guideline on SVT (7).

Atrial flutter

Atrial flutter is a rapid, organised electrical circuit—usually in the right atrium. It can cause a fast pulse and shares important issues with AF, including assessment of stroke risk. Medication, cardioversion or catheter ablation may be considered.

Bradycardia and heart block

A slow pulse is not automatically abnormal. However, if the heart’s natural pacemaker becomes unreliable or electrical signals are delayed or blocked, the heart rate may become insufficient. Symptoms can include fatigue, dizziness, breathlessness or blackouts. Some people need a pacemaker. The 2021 ESC pacing guideline (8) sets out evidence-based assessment and pacing indications.

Ventricular tachycardia and ventricular fibrillation

These rhythms begin in the ventricles. Ventricular tachycardia (VT) may reduce the heart’s ability to pump and can cause dizziness, fainting or cardiac arrest. Ventricular fibrillation (VF) is a medical emergency in which the ventricles quiver rather than pump effectively. Immediate CPR and defibrillation are required. Risk and treatment depend heavily on whether there is structural or inherited heart disease, as detailed in the 2022 ESC ventricular arrhythmia guideline (9).

What are the symptoms of arrhythmia?

Arrhythmia symptoms vary. You may experience:

• a racing, fluttering, pounding or irregular heartbeat;
• the sensation of a skipped or extra beat;
• dizziness or light-headedness;
• fainting or nearly fainting;
• shortness of breath;
• unusual tiredness or reduced exercise tolerance;
• chest discomfort;
• no symptoms at all.

Palpitations do not always mean an arrhythmia, and an arrhythmia does not always produce palpitations. Anxiety, anaemia, fever and an overactive thyroid can mimic or provoke rhythm symptoms. Equally, clinically important AF may be discovered incidentally. The NHS advice on heart palpitations (10) is a useful starting point, but recurring or concerning symptoms should be assessed.

When should I seek urgent help?

Call 999 if a rapid or irregular heartbeat is accompanied by:

• chest pain or pressure;
• severe difficulty breathing;
• fainting, collapse or inability to wake;
• sudden facial weakness, arm weakness or speech difficulty;
• prolonged severe symptoms or a feeling that something is seriously wrong.

If somebody is unresponsive and not breathing normally, call 999, start CPR and use an automated external defibrillator if available. For non-emergency symptoms that keep returning, are lasting longer or are getting worse, contact your GP or arrange a cardiology assessment. Do not drive yourself to emergency care if you feel faint or acutely unwell.

What causes arrhythmia?

Sometimes no single cause is found. Arrhythmias can also be associated with:

• ageing-related change in the heart’s electrical system;
• high blood pressure, coronary artery disease, previous heart attack, heart failure, valve disease or cardiomyopathy;
• an overactive or underactive thyroid;
• electrolyte disturbance, dehydration, fever or acute illness;
• sleep apnoea;
• alcohol, smoking, stimulant drugs or excessive caffeine in susceptible people;
• medicines, including some cold remedies and prescription drugs;
• pregnancy or hormonal change;
• inherited electrical conditions, such as long QT syndrome or Brugada syndrome;
• an extra electrical pathway present from birth.

Research describes AF as the product of interacting electrical and structural changes rather than a single mechanism (Schotten et al., 2011 (11)). This is why a thorough assessment looks beyond the rhythm strip to the person’s heart, health, medicines and lifestyle.

How is an arrhythmia diagnosed?

The central challenge is to record the heart rhythm while symptoms are occurring. A description such as “fluttering” is helpful but cannot identify the rhythm on its own.

A cardiology assessment usually begins with the timing, duration and triggers of symptoms; medical and family history; medicines and supplements; pulse and blood pressure; and a cardiovascular examination.

Tests may include:

1. 12-lead electrocardiogram (ECG). This quick, painless test records the heart’s electrical activity. The NHS ECG guide (12) explains what to expect.
2. Ambulatory ECG monitoring. A Holter monitor records continuously, often for 24–48 hours or longer. An event monitor or patch can be more useful when symptoms are intermittent. Longer monitoring increases the chance of capturing an infrequent rhythm; research after stroke shows how sequential monitoring can reveal otherwise missed AF (Sposato et al., 2015 (13)).
3. Echocardiogram. Ultrasound assesses the heart’s chambers, valves and pumping function.
4. Blood tests. These may check thyroid function, blood count, kidney function and electrolytes.
5. Exercise ECG or imaging. This may be appropriate if symptoms occur with exertion or coronary disease is suspected.
6. Implantable loop recorder. A small device under the skin can monitor the rhythm for years when significant but infrequent symptoms remain unexplained.
7. Electrophysiology study. In selected cases, fine catheters map the electrical circuit inside the heart and may be followed by ablation.

 

Figure 2 — ECG, ambulatory monitoring and echocardiography provide different information. The most appropriate test depends on the symptoms and how often they occur.

Can a smartwatch diagnose an arrhythmia?

A smartwatch can provide a useful clue, especially if it records a single-lead ECG during symptoms. Studies suggest good diagnostic accuracy for AF in suitable recordings (Nazarian et al., 2021 (14)). However, a watch is a screening tool, not a complete cardiac assessment. Motion, poor contact and ectopic beats can trigger misleading alerts, and dangerous rhythms can occur without a notification. Save relevant recordings and show them to a clinician rather than changing medication yourself.

How is arrhythmia treated?

Treatment depends on the exact rhythm, symptoms, underlying heart health and future risk. Not every arrhythmia needs treatment.

Treating contributing factors

Good care often includes managing blood pressure, thyroid disease, sleep apnoea, weight, diabetes and heart disease. Reducing binge drinking, stopping smoking, sleeping well and moderating stimulants may reduce symptoms for some people. Do not stop prescribed medicine without advice.

Medicines

Medicines may slow the heart rate, help maintain a normal rhythm or reduce episodes. In AF, anticoagulants can substantially reduce stroke risk for people who meet risk-based criteria. Anticoagulants do not “thin” blood in a literal sense or correct the rhythm; they reduce clot formation. Benefits and bleeding risk must be discussed individually. Device-detected AF burden has also been associated with stroke risk, although what a short device alert means requires clinical interpretation (Boriani et al., 2014 (15)).

Cardioversion

Cardioversion restores sinus rhythm using a controlled electrical shock under brief anaesthesia or, in some circumstances, medication. Planning includes checking the duration of AF and protecting against stroke.

Catheter ablation

During ablation, catheters are passed through a blood vessel to the heart. Heat or freezing energy targets the small area responsible for an abnormal rhythm. Ablation can be highly effective for many SVTs and atrial flutter and is an established option for selected patients with symptomatic AF or VT. Outcome and risk vary by rhythm and individual health.

Pacemaker or defibrillator

A pacemaker prevents the heart from beating too slowly. An implantable cardioverter-defibrillator (ICD) can detect and treat certain life-threatening ventricular rhythms. These devices have different purposes and are recommended only after careful assessment.

What can I do before my appointment?

A little preparation can make an arrhythmia consultation much more productive:

• Note when episodes start, how long they last and whether onset and offset are sudden.
• Record associated dizziness, fainting, chest discomfort or breathlessness.
• Check your pulse if safe, noting whether it feels regular or irregular.
• Save smartwatch ECGs, but do not rely on pulse-rate screenshots alone.
• List medicines, inhalers, supplements, caffeine, alcohol and any stimulant use.
• Ask relatives about unexplained young deaths, cardiomyopathy, pacemakers or inherited rhythm conditions.
• Avoid deliberately provoking symptoms.

Frequently asked questions

Is arrhythmia the same as palpitations?

No. Arrhythmia is an abnormal electrical rhythm; palpitations are the sensation of being aware of your heartbeat. You can have palpitations in a normal rhythm, and an arrhythmia without feeling it.

Is an irregular heartbeat always dangerous?

No. Ectopic beats are often harmless, and some slow heart rates are normal. However, AF can increase stroke risk and ventricular arrhythmias may be dangerous. The ECG diagnosis and clinical context determine significance.

Can stress cause arrhythmia?

Stress hormones can increase heart rate and make ectopic beats or existing arrhythmias more noticeable. Stress should not be assumed to be the cause until important cardiac and medical explanations have been considered.

Can caffeine cause arrhythmia?

Sensitivity varies. Moderate caffeine is tolerated by many people, but large doses—particularly energy drinks or stimulant combinations—may provoke palpitations. A symptom diary can help identify a consistent relationship.

Can arrhythmia be cured?

Some arrhythmias, particularly many SVTs and typical atrial flutter, can often be eliminated with ablation. Others, including AF, may recur and are better described as manageable. Treatment aims to improve symptoms and reduce important risks.

The cardiologist’s perspective

An unusual heartbeat is a symptom worth understanding, not a diagnosis to fear. The key is to capture the rhythm, assess the heart and the whole person, and match treatment to the actual level of risk. For many people, the outcome is reassurance. For others, timely diagnosis opens the door to effective medication, ablation or a cardiac device—and, in AF, potentially vital stroke prevention.

If you have recurrent palpitations, an irregular pulse, unexplained dizziness or reduced exercise tolerance, arrange a medical assessment. Bring any recordings and a symptom timeline: they may be the clues that make the diagnosis.

Research and clinical references

1. American Heart Association. What is an arrhythmia?
2. British Heart Foundation. Arrhythmias
3. NHS. Atrial fibrillation
4. National Institute for Health and Care Excellence. Atrial fibrillation: diagnosis and management (NG196)
5. Van Gelder IC, et al. 2024 ESC Guidelines for the management of atrial fibrillation. European Society of Cardiology, 2024.
6. NHS. Supraventricular tachycardia
7. Brugada J, et al. 2019 ESC Guidelines for supraventricular tachycardia. European Heart Journal. 2020;41:655–720.
8. Glikson M, et al. 2021 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy. European Heart Journal. 2021;42:3427–3520.
9. Zeppenfeld K, et al. 2022 ESC Guidelines for ventricular arrhythmias and prevention of sudden cardiac death. European Heart Journal. 2022;43:3997–4126.
10. NHS. Heart palpitations
11. Schotten U, Verheule S, Kirchhof P, Goette A. Pathophysiological mechanisms of atrial fibrillation. Physiological Reviews. 2011;91:265–325.
12. NHS. Electrocardiogram (ECG)
13. Sposato LA, et al. Diagnosis of atrial fibrillation after stroke and transient ischaemic attack: a systematic review and meta-analysis. The Lancet Neurology. 2015;14:377–387.
14. Nazarian S, et al. Diagnostic accuracy of smartwatches for the detection of cardiac arrhythmia: systematic review and meta-analysis. Journal of Medical Internet Research. 2021;23.
15. Boriani G, et al. Device-detected atrial fibrillation and risk for stroke. Heart Rhythm. 2014;11:1114–1120.