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Health condition · Clinically reviewed

Heart block, from a long PR interval to complete AV dissociation.

Not every heart block needs treatment, but knowing which type you have changes everything. A short guide to first, second and third-degree block and when a pacemaker earns its place.

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Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against ESC, NICE and Resuscitation Council UK sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK practice on pacing, ambulatory monitoring and treatment of the underlying cause.

Key facts

Heart block at a glance.

The essentials, in plain English. What each type means on the ECG, and what it changes in treatment.

  • What it is

    Impaired electrical conduction from the atria to the ventricles at the AV node or His-Purkinje system.

  • First-degree

    Prolonged PR interval over 200 milliseconds. Usually benign and no treatment needed.

  • Second-degree

    Mobitz I (Wenckebach) is usually benign. Mobitz II and high-grade forms carry a higher risk and often need pacing.

  • Third-degree

    Complete AV dissociation with a ventricular escape rhythm. A medical emergency and a firm pacing indication.

  • Common causes

    Ischaemic heart disease, conduction system fibrosis (Lenegre-Lev), medications, electrolytes and post-cardiac-surgery.

  • Definitive care

    Permanent pacemaker for symptomatic or high-risk block, alongside treatment of any reversible driver.

Why this guide matters

The label on the ECG changes the plan.

The classification of heart block is not academic. It tells clinicians which patients can be reassured and which need urgent pacing.

  • Not every block is the same

    First-degree and Wenckebach are usually benign. Mobitz II, high-grade and complete block are not.

  • Reversible causes matter

    Medications, potassium, ischaemia and infection can all drive block. Fixing the cause sometimes fixes the rhythm.

  • Pacing is safe and effective

    For symptomatic and high-risk block, a permanent pacemaker prevents blackouts and restores a normal life.

How the diagnosis is made

From the first ECG to a settled plan.

The steps a UK cardiologist will normally follow, in order, so you know what to expect and why each test earns its place.

  1. 01

    Assessing

    History and symptom review

    Fatigue, dizziness, syncope, palpitations and breathlessness plus a medication and family history for channelopathies.

  2. 02

    Assessing

    12-lead ECG

    The single most important test. Classifies the block and looks for ischaemia, bundle branch disease and QT changes.

  3. 03

    Assessing

    Bloods and reversible causes

    Potassium and other electrolytes, troponin if ischaemic, thyroid function and infection screen where relevant.

  4. 04

    Confirming

    Ambulatory monitoring

    Holter or an implantable loop recorder captures intermittent block that a single ECG can miss.

  5. 05

    Confirming

    Echocardiogram and cardiac MRI

    Looks for structural heart disease, cardiomyopathy, infiltration and fibrosis of the conducting tissue.

  6. 06

    Planning

    Electrophysiology study

    Selective and specialist commissioned. Localises the level of block in equivocal cases.

  7. 07

    Planning

    Specialist cardiology review

    Cardiology and electrophysiology decide on pacing, device selection and management of any underlying condition.

Typical timeline: from an ECG to a settled plan in days for high-risk block, weeks for slower presentations.

Symptoms

How heart block actually feels.

Anything from nothing at all to sudden blackouts. The features that push the diagnosis from watchful waiting to urgent care.

  • Often silent (first-degree)

    First-degree block is usually an incidental ECG finding with no symptoms at all.

  • Occasional palpitations

    Wenckebach (Mobitz I) may cause a sense of dropped or skipped beats, often felt at rest.

  • Fatigue and reduced exertion

    A slower ventricular rate can leave you tiring quickly on stairs and everyday tasks.

  • Dizziness and near-syncope

    Presyncope on standing or exertion is a warning sign in Mobitz II and higher-grade block.

  • Syncope (blackouts)

    Sudden loss of consciousness without warning. See our guide to fainting for context.

  • Stokes-Adams attacks

    Abrupt syncope with pallor followed by flushing as the heart restarts. A firm indication for pacing.

  • Breathlessness and heart failure

    A slow rate can trigger congestive symptoms, particularly in older or already-diseased hearts.

  • Red flag: cardiac arrest

    Prolonged pauses can trigger a cardiac arrest. Any collapse with no pulse needs immediate CPR and 999.

Treatment

How heart block is treated in the UK.

Watchful reassurance for benign forms, emergency stabilisation for complete block, and a permanent pacemaker for high-risk or symptomatic disease.

  • First-degree: observe

    Usually no treatment. Review any AV-blocking medications and reassure. Follow up if PR is very prolonged or symptoms appear.

  • Mobitz I: review and monitor

    Rationalise beta-blockers, calcium channel blockers and digoxin. Consider pacing only if syncope or symptoms are attributable.

  • Mobitz II and high-grade: pace

    Permanent pacemaker is the standard of care. Specialist electrophysiology decides device and lead configuration.

  • Complete heart block: pace

    A firm pacing indication in almost every case. Emergency stabilisation first, then permanent device.

  • Emergency stabilisation

    IV atropine, isoprenaline and temporary transcutaneous or transvenous pacing while the underlying cause is treated.

  • Treat the underlying cause

    Reperfusion for MI, potassium correction for hyperkalaemia, medication review and specialist care for endocarditis or Lyme.

  • CRT in selected patients

    Cardiac resynchronisation therapy for those with LV dysfunction and pacing needs. Specialist commissioned.

  • MDT and lifestyle support

    Cardiology, electrophysiology and, where useful, BHF and Cardiomyopathy UK for information and peer support.

For device details, see our guides to pacemaker implantation, implantable loop recorder and TAVR / TAVI. Related infection and structural drivers are covered on our endocarditis and cardiac arrest pages.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist society standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your cardiologist knows your history, your ECG and your medications and can tell you which parts apply to you. If you are unsure, get seen.

  • European Society of Cardiology (ESC). Guidelines on cardiac pacing and cardiac resynchronisation therapy.

  • NICE. Bradyarrhythmias and clinical knowledge summaries on syncope and heart block.

  • Resuscitation Council UK. Adult bradycardia algorithm and peri-arrest care.

  • British Heart Foundation and Cardiomyopathy UK. Patient information on heart block and pacemakers.

Red flags

When heart block needs urgent attention.

Some forms can be watched. These are the situations that cannot, and where a cardiology or emergency review is needed.

  • Syncope with no warning

    A blackout with no prodrome, particularly on exertion, points to a serious rhythm cause and needs urgent cardiology review.

  • Stokes-Adams attack

    Sudden collapse with pallor and then flushing as circulation returns. A firm indication for admission and pacing assessment.

  • Complete (third-degree) block on ECG

    Complete AV dissociation with a slow escape rhythm. Treat as an emergency and admit to a cardiac unit.

  • Mobitz II

    Higher risk of progression to complete block. Almost always needs inpatient pacing assessment even if symptoms are mild.

  • New block after inferior MI

    The AV node shares its blood supply with the inferior wall. New block after an inferior infarct needs prompt cardiology input.

  • Cardiac arrest or prolonged pauses

    Pauses over 3 seconds, or a collapse with no pulse, are emergencies. Start CPR and call 999.

  • New block after cardiac surgery or TAVI

    Conduction disease is a known risk after valve surgery and TAVI. Monitor closely and involve electrophysiology early.

  • Infective cause suspected

    Fever, murmurs or a tick-bite history raise endocarditis or Lyme carditis. Both need urgent specialist care.

  • Severe symptoms on medication

    New heart block on beta-blockers, calcium channel blockers, digoxin or amiodarone needs urgent medication review.

Living with it

A treatable rhythm, with a clear ladder.

Four things that make the biggest difference day to day. Know your ECG label, watch your medications, take symptoms seriously and accept a pacemaker if it is offered.

A quiet reminder

A pacemaker is not a limit. It is a licence to live normally.

Modern devices are small and reliable. For people with high-risk block they prevent blackouts and support an ordinary, active life.

  1. 01 Know

    Learn your ECG pattern

    Ask your cardiologist which type of block you have and what to watch for. Knowing the label makes information easier to find.

  2. 02 Meds

    Review AV-blocking drugs

    Beta-blockers, verapamil, diltiazem, digoxin and amiodarone can all worsen block. Any dose change should be discussed with a clinician.

  3. 03 Symptoms

    Take dizziness seriously

    Presyncope, syncope or a new drop in exercise tolerance deserves a same-week review, sooner if blackouts happen.

  4. 04 Pacemaker

    If a pacemaker is offered, accept

    Modern devices are small, reliable and largely invisible in daily life. They prevent blackouts and support a normal routine.

Frequently asked

Everything we get asked about heart block.

Quick answers on classification, causes, pacing and what to expect after treatment.

  • What is heart block?

    Heart block, or AV block, is a delay or failure of electrical signals travelling from the atria to the ventricles. It ranges from a benign prolonged PR interval on the ECG through to complete AV dissociation, which is a medical emergency.

  • Is first-degree heart block serious?

    For most people, no. It is usually an incidental ECG finding with no symptoms and no treatment needed. Very long PR intervals or those found alongside other conduction disease can still deserve a cardiology review, and any AV-blocking medications should be reviewed.

  • What is the difference between Mobitz I and Mobitz II?

    In Mobitz I (Wenckebach) the PR interval lengthens progressively until a beat is dropped. It is usually benign. In Mobitz II the PR interval stays constant and beats are dropped without warning. Mobitz II carries a much higher risk of progressing to complete block and almost always needs a pacemaker.

  • What causes complete heart block?

    Common causes include ischaemic heart disease, fibrosis of the conducting system (Lenegre-Lev), cardiomyopathy, medications, electrolyte disturbance, infection such as endocarditis or Lyme carditis, infiltrative disease such as amyloid or sarcoid, congenital block (including neonatal lupus) and complications of valve surgery or TAVI.

  • When is a pacemaker needed?

    A permanent pacemaker is standard for symptomatic Mobitz I, Mobitz II, high-grade AV block and complete heart block. The decision is made by a specialist cardiologist or electrophysiologist after ECG, ambulatory monitoring and imaging.

  • Can heart block be treated by fixing the cause?

    Sometimes. Block from an acute MI, hyperkalaemia, Lyme carditis or a rate-slowing drug can resolve once the underlying problem is corrected. In many other cases, particularly conduction system fibrosis, block is permanent and pacing is the definitive treatment.

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