Right bundle branch block (RBBB): what complete and incomplete RBBB mean on an ECG

Short answer

A right bundle branch block (RBBB) is an ECG finding, not a diagnosis of heart disease: the electrical signal reaches the right ventricle a little later than usual, so the QRS complex looks wider and has a characteristic shape. StatPearls describes it as an electrocardiogram finding that usually causes no symptoms and is typically found by chance on an ECG done for another reason (1). Incomplete RBBB is the milder version. In the Copenhagen City Heart Study of 18,441 adults it was found in 4.7% of men and 2.3% of women and was not associated with any adverse outcome; complete RBBB was associated with higher all-cause and cardiovascular mortality (3).

If the words "block" and "heart" on the same printout frightened you, you are not alone: here "block" describes a delay in electrical conduction, not a blocked artery (1). Incomplete RBBB is a common ECG finding, and international criteria for athletes treat it as normal and training-related (5). It is also not your fault: we found no research tying it to a bad night, a stressful week or anything you did before the test.

Note: this article explains what research and clinical guidelines say and is not medical advice. It cannot interpret your ECG or tell you what your result means for you. Fainting, chest pain or shortness of breath is a 911 call, and a new right bundle branch block that comes with symptoms needs a clinician the same day.

What is a right bundle branch block?

A right bundle branch block means the right bundle branch, one of two wiring paths carrying each heartbeat's signal into the ventricles, conducts slowly or not at all. The heart still beats; the right ventricle is activated later.

Normally the signal splits into the right and left bundle branches and both ventricles are activated almost together, so the QRS complex is narrow. When the right bundle is altered or interrupted, the signal goes down the left side first and spreads through muscle to the right ventricle, which is slower. The QRS widens, and its final part points toward the right ventricle (1, 2).

Our guide to what an EKG (ECG) is explains the P wave, QRS complex and T wave.

What is RBBB in medical terms?

In medical terms, RBBB is an intraventricular conduction disturbance: a delay in how the electrical impulse spreads through the ventricles. That is how the AHA/ACCF/HRS ECG recommendations classify it (2). It describes a pattern on the tracing, not its cause.

Is right bundle branch block an arrhythmia?

Not in the usual sense. An arrhythmia is a problem with the rate or rhythm of the heartbeat; RBBB is a problem with the path the signal takes once a beat has started. Someone with RBBB can be in an entirely regular sinus rhythm. If you have palpitations, our overview of heart arrhythmia symptoms covers what those feel like.

Complete vs incomplete right bundle branch block: what's the difference?

The difference is mostly the width of the QRS complex. Complete RBBB is defined in adults by a QRS of 120 milliseconds or more with the typical right-sided pattern; incomplete RBBB has the same shape with a QRS just under that (2).

What is an incomplete right bundle branch block?

An incomplete right bundle branch block is a right-bundle-branch-block shape on the ECG with a QRS that is only slightly wider than normal. A 2025 narrative review describes it as a frequent ECG finding that is often considered benign, with prevalence between 2% and 8% depending on the population, and higher in men, athletes and people with chronic lung disease (6). Reports often abbreviate it IRBBB.

What does RBBB look like on ECG? Reading a right bundle branch block ECG

On a right bundle branch block ECG, the clinician looks at three things: a wide QRS, an "M-shaped" or rabbit-ear complex in the right-sided chest leads, and a broad, slurred S wave in the left-sided leads. This article cannot apply them to your own tracing.

The AHA/ACCF/HRS criteria for complete RBBB in adults are (2):

StatPearls adds that the T wave tends to point the opposite way to the end of the QRS (1).

A smartwatch records a single lead, not twelve views; our article on an Apple Watch ECG that says inconclusive explains what one lead can and cannot classify.

What causes right bundle branch block?

Often nothing that needs treating: in many athletes, incomplete RBBB appears to reflect a larger right ventricle rather than disease (4). When there is a cause, clinical sources describe these:

• Age-related fibrosis of the conduction system, also called Lenègre's or Lev's disease (1).

• Right ventricular pressure or volume load: pulmonary embolism, chronic lung disease, pulmonary hypertension and atrial septal defect, a congenital opening between the atria (1, 6).

• Heart muscle injury or inflammation: heart attack, myocarditis and infiltrative diseases (1).

• Electrolyte disturbances, rarely high potassium (1, 6).

• Procedures, such as right heart catheterization (1).

• Uncommon inherited conditions, such as Brugada syndrome and arrhythmogenic right ventricular cardiomyopathy, which can first show an incomplete-RBBB-like pattern; these are not frequent and usually come with other ECG or imaging findings (6).

In the Copenhagen cohort, newly acquired incomplete RBBB was predicted by male sex, older age and low body mass index (3).

What medications can cause right bundle branch block?

The 2018 ACC/AHA/HRS bradycardia and conduction guideline includes a table of medications that can induce or worsen bradycardia or conduction disorders. It is a broad category, not specific to RBBB, and includes antiarrhythmics such as flecainide, propafenone, procainamide, quinidine, amiodarone and sotalol; beta-blockers, including eye drops for glaucoma; non-dihydropyridine calcium channel blockers; and psychoactive drugs such as tricyclic antidepressants, lithium and some antipsychotics (11). For one of them the US prescribing information is specific: "In one study, 4% of patients developed new bundle branch block while on flecainide acetate" (12); the label does not say which side.

Do not stop any medicine on your own — talk to your prescriber. Bring a full list, including eye drops, so the prescriber can judge whether a medicine fits the timing.

Is right bundle branch block serious?

Whether RBBB is dangerous depends on which kind, and on the person. In a large general-population study, incomplete RBBB was not associated with any adverse outcome, while complete RBBB was associated with higher cardiovascular risk and all-cause mortality on average (3).

The Copenhagen City Heart Study followed 18,441 adults free of prior heart attack, heart failure and left bundle branch block:

A hazard ratio is a relative comparison, not your personal chance. The authors concluded that complete RBBB without symptoms should still prompt clinicians to think about cardiovascular risk (3). StatPearls gives the other side: "In patients without significant heart disease, right bundle branch block does not have any additional risk" (1). Both are true: complete RBBB is a reason to look, not a verdict.

Keeping notes while you wait for an appointment is fine, but fainting, chest pain or pressure, or shortness of breath is a 911 call, not a diary entry (13, 14).

Is incomplete RBBB dangerous?

In general-population research, incomplete RBBB has not been linked to worse outcomes. In the Copenhagen cohort, "the presence of IRBBB was not associated with any adverse outcome" (3). A 2025 review cautions that it can matter more in people with lung disease, pulmonary hypertension or structural heart disease, and states: "In asymptomatic individuals with incidentally discovered iRBBB and no cardiovascular risk factors, further testing is usually not required" (6). Whether that describes you is your clinician's call.

Incomplete RBBB in young, healthy people and athletes

In trained athletes, incomplete RBBB is common and appears to reflect a larger right ventricle. In a study of 510 competitive athletes, 9% had incomplete and about 3% had complete RBBB; both groups had larger right ventricles than matched athletes with a normal QRS, and none had structural heart disease (4).

The authors read these patterns as markers of right-ventricular remodeling. The 2017 international criteria for interpreting athletes' ECGs list incomplete RBBB among normal training-related findings and state that "incomplete RBBB represents a phenotype of cardiac adaptation to exercise" that, without other signs of disease, needs no further evaluation (5). Complete RBBB is "borderline": alone, in an athlete without symptoms or a family history of premature cardiac disease or sudden death, the statement does not call for further assessment; combined with another borderline finding it counts as abnormal (5). This framing was written for athletes; it does not mean every young person's incomplete RBBB comes from training.

Right bundle branch block and exercise

Exercise is linked to RBBB in two ways. Long-term training is associated with incomplete RBBB through right-ventricular remodeling (4). Separately, a block can appear during exercise as the heart rate rises, a different and much rarer finding (see the next section). Whether to change your training is your clinician's call. Same rule beside the training advice: fainting, chest pain or unusual shortness of breath during exercise means stopping and calling 911 (14).

Why RBBB can show up on one ECG and not the next

Three documented reasons can explain "it was there, then it wasn't."

1. Where the chest electrodes went. Leads V1 and V2 are meant to sit in the fourth intercostal space, either side of the breastbone. An emergency-medicine review notes that V1 and V2 are often misplaced, that "such misplacement usually involves placing these leads too high on the chest," and that the result can include a false incomplete RBBB pattern (7). A cardiology letter describes an rSr′ pattern recorded with V1 in the second intercostal space that disappeared when the electrodes were moved to the fourth, and warns against reading it as RBBB (8).

2. Heart rate. Some bundle branch blocks are rate-dependent: they appear only at faster heart rates. StatPearls notes that a tachycardia-dependent bundle branch block can occur when, at a high heart rate, the conduction tissue cannot recover in time for the next impulse (1). Among 9,623 veterans having routine treadmill tests, exercise-induced RBBB occurred in 0.24%, and the authors called it "a rare occurrence during routine clinical exercise testing that appears to be benign" (9). An older series reached a different conclusion: all 13 patients with exercise-induced RBBB had significant coronary artery disease (10). Both studied patients referred for exercise testing, not healthy young adults; the research on what rate-related block means is mixed.

3. A measurement near a line. Incomplete RBBB is defined by a QRS width within a narrow band, and the band itself differs slightly between sources (2, 1). A few milliseconds can change the label.

A transient pattern can also appear during an acute illness, such as a pulmonary embolism or a heart attack (6). That is why a new RBBB with symptoms is treated differently from an old one found by chance.

Can a right bundle branch block go away?

Sometimes the pattern does. It can come and go with electrode placement (7, 8), with heart rate in rate-dependent block (1), or after an acute condition such as a pulmonary embolism settles (6). We did not find studies measuring whether it fades after athletes stop training, so we cannot say. In the Copenhagen cohort, incomplete RBBB was also one of the predictors of later complete RBBB (3).

Can anxiety cause right bundle branch block?

We found no study showing that anxiety causes right bundle branch block, and anxiety does not appear among the causes listed in clinical sources (1, 6).

What can be said with evidence is narrower. Rate-dependent bundle branch block appears at faster heart rates (1), and in a large exercise-testing study exercise-induced RBBB was rare (9). No study we found tested whether anxiety's faster heart rate brings out an RBBB pattern. Anxiety can still make living with this finding much harder, and that deserves attention in its own right.

Can stress, poor sleep or night shifts cause RBBB?

We did not find any study testing whether stress, short sleep or shift work changes a right bundle branch block, so we cannot say that they do or that they do not. If a finding seems to come and go with your schedule, write down the date, time and circumstances of each ECG for your clinician. Electrode placement and heart rate at the moment of recording are the documented explanations to rule out first (7, 1).

Right bundle branch block symptoms

Right bundle branch block itself usually causes no symptoms. StatPearls describes it as usually asymptomatic and typically discovered on an ECG done for another reason (1). Symptoms usually come from whatever is causing the block, which is why they change the picture. The 2025 review lists exertional breathlessness, palpitations, fainting and a family history of sudden cardiac death or inherited cardiomyopathy as reasons a focused evaluation is warranted (6).

• Fainting, chest pain or pressure, severe shortness of breath — Call 911 (13, 14)

• A new RBBB on an ECG done because you had symptoms — Contact a clinician the same day

• Palpitations, near-fainting, breathlessness on exertion, family history of sudden death — Book a prompt appointment

• Incomplete RBBB found by chance, no symptoms — Ask at your next visit what it means for you

Right bundle branch block treatment: when it's needed

Right bundle branch block on its own is usually not treated; when treatment is needed, it targets the underlying cause or a more serious conduction problem. StatPearls states that isolated RBBB without symptoms generally does not require further evaluation or treatment (1).

The 2018 ACC/AHA/HRS guideline on bradycardia and conduction delay sets out what clinicians consider (11):

• Look for a reversible or underlying cause first, such as ischemia.

• Echocardiography is described as reasonable for RBBB when structural heart disease is suspected, a weaker recommendation than for newly identified left bundle branch block, where it is recommended.

• Ambulatory ECG monitoring if symptoms suggest intermittent slow heart rhythms.

• Permanent pacing is reserved for specific situations, such as fainting with bundle branch block plus a prolonged conduction time measured in an electrophysiology study, or bundle branch block that alternates between the right and left sides. Otherwise: observation.

None of that is a recommendation from us. Which tests make sense depends on your symptoms, history and the rest of your ECG; your clinician decides which, if any, apply to you.

When to see a doctor about right bundle branch block

See a doctor promptly if an RBBB is new and you have symptoms, if it is complete and you have not yet discussed it with a clinician, or if you have a family history of sudden cardiac death. Call 911 for fainting, chest pain or pressure, or shortness of breath (13, 14).

• Same day: a new RBBB with palpitations, dizziness, unusual breathlessness or chest discomfort. A transient RBBB pattern can appear in acute conditions such as pulmonary embolism (6).

• Soon: complete RBBB found by chance. The Copenhagen authors wrote that, even without symptoms, it should alert clinicians to cardiovascular risk (3).

• At a routine visit: incomplete RBBB, no symptoms, no family history. A 2025 review says that with no symptoms and no cardiovascular risk factors, further testing is usually not required (6); your clinician decides whether that applies to you, and having it noted lets future ECGs be compared with it.

Living with right bundle branch block: the questions people ask next

Can I keep exercising with right bundle branch block?

International criteria for athletes do not treat isolated RBBB by itself as a reason to stop training, but your training is your clinician's call. International criteria for athletes classify isolated incomplete RBBB as a normal adaptation to training that needs no further evaluation, and complete RBBB as a borderline finding that needs more assessment only with symptoms, a family history or other borderline findings (5). Fainting, chest pain or unusual breathlessness during exercise is a 911 call (13, 14).

Will incomplete RBBB turn into complete RBBB?

It can, though research does not give an individual's odds. In the Copenhagen City Heart Study, incomplete RBBB was one of the predictors of later complete RBBB, alongside male sex, older age and high systolic blood pressure (3). The same study found incomplete RBBB itself was not associated with any adverse outcome. Keeping a copy of your ECG lets a future clinician compare.

Should I do squats before an ECG so the block doesn't show?

No. We found no study testing whether squats, or any exercise right before an ECG, changes a right bundle branch block pattern, and we do not suggest it. A resting ECG is meant to show your heart at rest. The documented reasons a pattern varies between ECGs are electrode placement, especially V1 and V2 placed too high (7), and heart-rate-dependent block (1). If you suspect a placement artifact, ask whether the ECG can be repeated.

Is RBBB considered heart disease?

Not by itself. Right bundle branch block is an ECG finding, a description of how the electrical signal travels through the ventricles (1, 2). It can occur in healthy hearts, especially as incomplete RBBB in athletes, where no structural disease was found in one study of 510 athletes (4). It can also be a sign of an underlying problem, such as lung disease, a congenital heart defect or age-related wear of the conduction system (1, 6). A clinician's assessment, sometimes with an echocardiogram, answers whether anything lies behind it.

Why did one doctor say it was nothing and another ordered an echo?

Because both responses can fit the evidence, depending on what each clinician saw. A 2025 review says incomplete RBBB found by chance, without symptoms or cardiovascular risk factors, usually needs no further testing (6). For RBBB more broadly, the 2018 ACC/AHA/HRS guideline describes echocardiography as reasonable when structural heart disease is suspected (11), which leaves room for judgment. Complete RBBB carries more weight in population studies than incomplete (3). If it confuses you, ask each clinician what they were ruling out.

I can't stop worrying about this finding. Is that normal?

Very. "Block" sounds like a blockage, and a printout without explanation leaves room for the imagination. The words describe a delay in electrical conduction, not a blocked artery (1). If worry is affecting sleep, work or exercise, say so at the appointment: a clear explanation of your result is part of good care. And if worry comes with chest pain, fainting or breathlessness, do not decide alone whether it is anxiety: call 911 (13).

How to bring this up with your doctor

Say it in one sentence first: "My ECG report says [incomplete / complete] right bundle branch block, and I want to understand whether it needs anything, given my history."

Bring the ECG itself, not just the summary line. Bring older ECGs too: whether the finding is new or old matters a lot.

Bring a short written record. Any symptoms and when they happen, especially palpitations, dizziness, fainting or breathlessness on exertion; how much and what kind of exercise you do; any family history of sudden death, cardiomyopathy or pacemakers; and every medicine you take, including eye drops (11).

Questions worth asking:

• "Is this complete or incomplete RBBB, and is anything else on the ECG worth following?"

• "Could electrode placement or my heart rate at the time explain why it shows on some ECGs and not others?"

• "Given my history, do I need an echocardiogram or any other test, or is this something to note and watch?"

• "Are any of my medicines relevant here?" — and do not stop any medicine on your own.

• "Are there symptoms that should make me call you the same day or go to the emergency room?"

And do not save these for the appointment. Fainting, chest pain or pressure, or shortness of breath means calling 911 now. A new RBBB that comes with symptoms means contacting a clinician the same day (13, 14).

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How Welltory helps — and what it cannot do

The limits come first. Welltory is a general wellness product, not a medical device. It does not diagnose, detect, predict, monitor, prevent, treat or mitigate any condition, including bundle branch block. Welltory does not record or read ECGs and cannot see or rule out a right bundle branch block; its heart rate and HRV readings are not an ECG and cannot replace one. What it offers is a personal record that sits beside the ECG your clinician reads.

You note the moment; the app records the numbers around it. When a stress stretch appears on your Today screen and the app asks "What happened?", you can tap a suggested tag, type a few words or just talk: "got ECG results", "palpitations", "dizzy standing up", "hard interval session", "night shift", "short night", "worried about heart". You know what happened. The app keeps the time and the heart data around it.

Then look at the days around it. Resting heart rate, HRV, sleep analysis, stress minutes and Battery are recorded the same way every day. A tagged moment can be read next to your own history, such as the night before, rather than against a population chart or a line marked normal. Stress minutes, sleep analysis and Battery need a supported wearable; with a phone-camera (PPG) reading alone, you have your spot measurements. None of these numbers says anything about how the signal travels through your ventricles.

After two to three weeks of tagging, My Patterns has something to work with. My Patterns collects the tags you add to stress and rest stretches on the Today screen, so it needs iOS with an Apple Watch or Oura. Patterns appear at around seven tagged events in the current month, with some history from the month before. It shows which tagged situations tend to come alongside stressful stretches, which tags do not happen often but hit your body hard, trends by day of week, heart-rate data, and every time a tag occurred.

That list is what you take to the appointment, next to the ECG. The Journal (Premium) keeps your measurements, tags and notes. From the Welltory web app you can export a CSV (Dashboard → choose a chart → Export). Together it becomes a diary: you noted it, the app recorded it. Any pattern in it is an association to discuss with your doctor, not proof of a cause and not a warning system.

The red flags belong here too, in the same type size: fainting, chest pain or pressure, or shortness of breath is a 911 call. A new right bundle branch block that comes with symptoms means contacting a clinician that day, not adding a tag (13, 14).

How we made it

Made with AI tools, then edited and fact-checked by the Welltory team. See our Editorial & AI policy.

Data analysis by Jane Smorodnikova, co-founder of Welltory and the person who built the methodology behind how we read physiological data.

Written by Tatsiana Yashyna.

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