A right bundle branch block (RBBB) is a delay in the electrical signals that tell the right side of your heart to squeeze. It almost never causes symptoms on its own and is usually discovered by accident during a routine electrocardiogram (ECG). In people without underlying heart disease, it’s generally not serious, but it can sometimes be an early marker of changes in the heart that deserve follow-up.
How Your Heart’s Electrical System Works
Every heartbeat starts with an electrical impulse at the top of the heart. That impulse travels down through a structure called the bundle of His, which splits into two pathways: a left bundle branch (serving the left ventricle) and a right bundle branch (serving the right ventricle). These branches carry the signal almost simultaneously so both sides of the heart contract in sync.
When the right bundle branch is partially or fully blocked, the electrical signal has to detour through regular heart muscle tissue instead of the fast-track wiring. Muscle tissue conducts electricity more slowly, so the right ventricle contracts a fraction of a second behind the left. That timing mismatch is what shows up on an ECG and earns the name “right bundle branch block.”
What It Looks Like on an ECG
Doctors diagnose RBBB by reading the shape and width of the QRS complex, the portion of each ECG tracing that represents the ventricles contracting. A complete RBBB produces a QRS complex wider than 120 milliseconds and a characteristic M-shaped pattern in the leads that look at the right side of the heart (V1 and V2). That M shape reflects the right ventricle activating late, creating a second upward deflection in the tracing.
An incomplete RBBB shows the same M-shaped pattern but with a narrower QRS, typically between 90 and 120 milliseconds. This means the signal is slowed but not fully blocked. Incomplete RBBB is even more common and is generally considered a normal variant, especially in younger people and athletes.
Common Causes
RBBB can appear in a completely healthy heart. In many cases, no underlying cause is ever identified, particularly in younger adults. But several conditions can damage or stress the right bundle branch enough to slow conduction:
- Blood clot in the lungs (pulmonary embolism): sudden strain on the right side of the heart can produce a new RBBB.
- Heart attack: damage to heart tissue near the conduction system can disrupt the pathway.
- Congenital heart defects: a hole between the upper chambers of the heart (atrial septal defect) is a classic cause.
- High blood pressure in the lung arteries (pulmonary hypertension): chronic pressure overload on the right ventricle can eventually affect the wiring.
- Inflammation of the heart muscle (myocarditis): infections or autoimmune conditions that inflame heart tissue can interfere with electrical conduction.
Age-related wear on the conduction system is probably the most common explanation overall. The prevalence of RBBB rises steeply as people get older: roughly 1% of men at age 50, about 5% by age 67, and over 11% by age 80, according to a long-running study published in the AHA journal Circulation.
Symptoms
Most people with RBBB feel nothing at all. The slight delay in right ventricular contraction is too small to affect how well the heart pumps in everyday life. The block is typically spotted during a routine physical or an ECG done for an unrelated reason.
Rarely, someone with RBBB may experience fainting or a feeling of nearly fainting. When that happens, the concern is usually about an underlying heart condition rather than the block itself. New symptoms like chest pain, sudden breathlessness, or swelling in the legs alongside a known RBBB are worth prompt medical attention because they could point to a developing problem like heart failure or a pulmonary embolism.
Is It Serious?
The short answer depends on context. If you have no symptoms and no known heart disease, an isolated RBBB is not considered dangerous. Many people live their entire lives with one and never need treatment.
The picture changes when RBBB appears alongside existing cardiovascular disease. In people experiencing a heart attack, RBBB is an independent predictor of worse outcomes, including higher in-hospital mortality. In heart failure, it signals more advanced disease and a greater risk of death. A study in the Journal of the American Heart Association found that even in people without known cardiovascular disease, RBBB was associated with a 50% higher risk of death from any cause and a 70% higher risk of cardiovascular death after adjusting for other risk factors like age, diabetes, high blood pressure, and smoking.
Researchers believe this is because RBBB can be an early signal of subtle heart muscle changes, including conditions like amyloidosis (abnormal protein deposits), sarcoidosis (inflammatory granulomas), or progressive fibrosis in the conduction system. These conditions may not produce obvious symptoms early on but can eventually lead to more serious rhythm problems or heart failure.
Exercise and RBBB
Some people develop RBBB only during exercise, a pattern called exercise-induced RBBB. It is rare, occurring in about 0.27% of people undergoing stress testing. Unlike a resting RBBB found incidentally, exercise-induced RBBB is considered more concerning and typically prompts further cardiac evaluation to rule out underlying coronary artery disease or structural problems.
Having a resting RBBB does not mean you need to avoid exercise. For the vast majority of people with an incidental finding, physical activity remains safe. Athletes, in particular, frequently show incomplete RBBB patterns that reflect normal adaptations of a well-trained heart rather than disease.
What Happens After Diagnosis
If your ECG shows an RBBB and you have no symptoms or history of heart disease, your doctor may not recommend any treatment at all. In many cases, the finding is simply noted in your chart and monitored over time.
When there is reason to suspect an underlying cause, your doctor will likely order additional testing. An echocardiogram (heart ultrasound) can check for structural problems like a septal defect or signs of right ventricular strain. Blood tests or imaging may follow if conditions like pulmonary embolism or myocarditis are suspected.
RBBB itself has no specific treatment because the block is in the wiring, not in a valve or artery. If it progresses to involve both bundle branches (called bifascicular or trifascicular block), or if it’s associated with dangerously slow heart rhythms, a pacemaker may eventually be needed. This progression is uncommon, but it’s one reason doctors track conduction patterns over time, especially in older adults or people with other cardiac risk factors.