S4: Definition, Clinical Significance, and Overview

Posted on February 28, 2026 | by drheartcare

S4 Introduction (What it is)

S4 is the fourth heart sound, an extra low-frequency sound heard in late diastole.
It reflects atrial contraction against a stiff or noncompliant ventricle.
It is a bedside clinical finding in cardiovascular examination (auscultation).
It is most commonly discussed in the assessment of hypertension, cardiomyopathy, and diastolic dysfunction.

Clinical role and significance

S4 matters because it can be a clue to abnormal ventricular filling and reduced ventricular compliance. In practical terms, it is a physical exam marker that may support suspicion of left ventricular hypertrophy (LVH), ischemic heart disease, hypertrophic cardiomyopathy, or other conditions that impair diastolic relaxation and compliance.

In many patients, S4 is not diagnostic by itself, but it can add “weight” to the overall clinical picture when combined with symptoms (e.g., dyspnea on exertion, chest pain), other exam findings (murmurs, displaced point of maximal impulse), and tests such as electrocardiography (ECG) and echocardiography. For learners, S4 is also exam-relevant because it helps distinguish patterns of heart sounds (S1, S2, S3, S4), timing within the cardiac cycle, and how auscultation correlates with cardiac physiology.

S4 is sometimes described as an “atrial gallop.” Its presence suggests that the atria are contributing a noticeable final “push” to ventricular filling (the atrial kick) because the ventricle is relatively stiff. This concept often overlaps with evaluation of heart failure with preserved ejection fraction (HFpEF), long-standing hypertension, and aortic stenosis, where diastolic abnormalities are common.

Indications / use cases

Typical scenarios where clinicians listen for or discuss S4 include:

Evaluation of suspected diastolic dysfunction (including HFpEF) in patients with exertional dyspnea
Long-standing systemic hypertension with concern for LVH
Assessment of aortic stenosis or other causes of pressure overload
Workup of cardiomyopathies, including hypertrophic cardiomyopathy
Chest pain presentations where ischemia or prior myocardial infarction is a consideration (context-dependent)
Bedside characterization of abnormal heart sounds alongside murmurs and gallops
Teaching and exam settings to reinforce timing of heart sounds within the cardiac cycle
Correlation with ECG findings (e.g., LVH patterns) and echocardiographic measures of diastolic function

Contraindications / limitations

There are no true contraindications to listening for S4, since auscultation is noninvasive.

The most relevant limitations are interpretive and physiologic:

S4 cannot be generated in atrial fibrillation because there is no coordinated atrial contraction (no effective atrial kick).
Tachycardia can make timing difficult and may cause summation phenomena (S3 and S4 merging), reducing reliability.
Obesity, chronic obstructive pulmonary disease (COPD), chest wall thickness, and ambient noise can reduce audibility.
Differentiating S4 from a split S1, an ejection click, or a short diastolic murmur can be challenging without experience.
S4 is neither highly sensitive nor specific for any single diagnosis; it should be interpreted with history, exam, and confirmatory testing (often echocardiography).
Right-sided S4 can be subtle and may require focused technique; its intensity may vary with respiration.

How it works (Mechanism / physiology)

Mechanism / physiologic principle

S4 occurs in late diastole, just before S1. It is produced when atrial contraction forces blood into a ventricle that has reduced compliance (is “stiffer” than expected). This late diastolic filling event creates vibrations in the ventricular wall and surrounding structures that can be perceived as a low-frequency sound.

A useful timing summary is:

S1: closure of the mitral and tricuspid valves (start of systole)
S2: closure of the aortic and pulmonic valves (end of systole)
S3: early diastolic filling sound (rapid passive filling)
S4: late diastolic filling sound (atrial contraction)

Clinically, S4 is most often linked to decreased ventricular compliance rather than increased volume alone.

Relevant cardiac anatomy and structures

Atria: provide the final contribution to ventricular filling via atrial systole.
Ventricular myocardium: reduced compliance can result from hypertrophy (pressure overload), fibrosis, ischemia, or infiltrative processes.
Atrioventricular (AV) valves: S4 is not primarily a valve closure sound (unlike S1/S2), but valve position and ventricular filling dynamics affect transmission and audibility.
Left ventricle vs right ventricle: left-sided S4 is more commonly appreciated; right-sided S4 may be heard along the left lower sternal border and can vary with inspiration.

Onset, duration, and reversibility (as applicable)

S4 is an auscultatory finding rather than a therapy, so “onset” and “duration” apply mainly to the underlying physiology. An S4 may appear or become more prominent when ventricular compliance worsens (e.g., increasing hypertrophy, ischemia, rising filling pressures). It may diminish if the underlying condition improves or if the rhythm changes (for example, development of atrial fibrillation eliminates a true S4). The presence and intensity can vary by clinician technique, patient position, and hemodynamic state.

S4 Procedure or application overview

S4 is not a procedure; it is assessed during the cardiovascular physical examination and integrated with diagnostic testing.

A general workflow is:

Evaluation / exam – Obtain symptoms and context (dyspnea, chest pain, syncope, hypertension history). – Inspect, palpate, and then auscultate systematically (aortic, pulmonic, tricuspid, mitral areas).
Focused auscultation for timing – Identify S1 and S2 first. – Use the carotid upstroke as a timing reference (S1 occurs just before the upstroke; S4 occurs just before S1).
Optimize listening conditions – Use the bell of the stethoscope for low-frequency sounds like S4. – For a suspected left-sided S4, listen at the apex with the patient in the left lateral decubitus position. – For a suspected right-sided S4, listen near the left lower sternal border and note respiratory variation (findings can vary with inspiration).
Immediate checks – Consider the rhythm: a regular rhythm supports the possibility of a true S4, while atrial fibrillation argues against it. – Distinguish from other sounds: split S1, S3, clicks, or murmurs.
Diagnostics (as appropriate to the clinical scenario) – ECG for rhythm (e.g., atrial fibrillation), LVH patterns, ischemic changes. – Echocardiography to assess LVH, valve disease (e.g., aortic stenosis), and diastolic function. – Additional tests vary by clinician and case.
Follow-up / monitoring – Reassess symptoms and correlate with objective data (blood pressure trends, echocardiographic parameters, functional status).

Types / variations

Common clinically relevant variations of S4 include:

Left-sided vs right-sided S4
Left-sided S4 is more commonly detected and is associated with conditions affecting left ventricular compliance (e.g., hypertension with LVH, aortic stenosis, hypertrophic cardiomyopathy).
Right-sided S4 can occur with reduced right ventricular compliance (e.g., pulmonary hypertension, pulmonic stenosis), and may show respiratory variation.
Physiologic vs pathologic framing
S4 is generally taught as more suggestive of pathology than S3, especially in older patients, but the clinical meaning depends on context and comorbidities.
Audible bedside S4 vs recorded/assisted detection
In some settings, phonocardiography or digital stethoscopes may help with timing and teaching, but clinical interpretation still requires correlation with the patient’s condition and other tests.
Isolated S4 vs S4 with other findings
S4 may be heard alongside a systolic murmur (e.g., aortic stenosis) or with other abnormal heart sounds.
With tachycardia, summation gallop may occur when S3 and S4 merge, complicating interpretation.

Advantages and limitations

Advantages:

Noninvasive bedside clue to altered ventricular compliance and late diastolic filling dynamics
Can be assessed rapidly during routine cardiac auscultation without equipment beyond a stethoscope
Helps learners localize timing within the cardiac cycle (late diastole, just before S1)
Supports clinical suspicion for conditions like LVH, aortic stenosis, or hypertrophic cardiomyopathy when consistent with the overall presentation
Encourages integration of exam findings with ECG and echocardiography rather than reliance on a single data point
May be useful for longitudinal comparison in the same patient when exam conditions are similar

Limitations:

Not present in atrial fibrillation (no coordinated atrial contraction), limiting utility in common arrhythmias
Low-frequency and often subtle; detection varies with examiner experience, patient body habitus, and ambient noise
Limited specificity; multiple conditions can produce a similar late diastolic sound
Can be confused with split S1, S3, clicks, or short murmurs, especially at higher heart rates
Does not quantify severity of diastolic dysfunction or filling pressures on its own
May change with hemodynamics (volume status, blood pressure, ischemia), so a single exam is a snapshot

Follow-up, monitoring, and outcomes

S4 itself is an exam finding, so “outcomes” relate to the underlying cardiac condition rather than the sound. Monitoring generally focuses on the trajectory of symptoms, hemodynamics, rhythm status, and structural heart disease.

Key factors that commonly affect interpretation and follow-up include:

Severity and cause of reduced compliance: LVH from hypertension, valvular stenosis, ischemia-related stiffness, or cardiomyopathy can all influence whether S4 is present and how meaningful it is.
Cardiac rhythm: development of atrial fibrillation removes the atrial contribution to filling and eliminates a true S4, while restoration of sinus rhythm can allow S4 to reappear (context-dependent).
Blood pressure and afterload: pressure overload states can reinforce the physiology associated with S4; response to management varies by clinician and case.
Comorbidities: chronic lung disease, obesity, anemia, kidney disease, and sleep-disordered breathing can alter symptoms and exam conditions, complicating bedside assessment.
Imaging correlation: echocardiographic findings (LV wall thickness, left atrial size, diastolic indices, valve gradients) often determine prognosis and guide monitoring more reliably than auscultation alone.
Functional status: exercise tolerance and signs of congestion provide practical context, especially in suspected HFpEF.

In many real-world settings, clinicians document S4 as part of a broader cardiovascular assessment and then prioritize objective confirmation (often echocardiography) when structural or functional disease is suspected.

Alternatives / comparisons

Because S4 is a clinical sign rather than a treatment, “alternatives” are best understood as other ways to evaluate similar physiology or competing explanations for symptoms.

S4 vs S3
S4 is linked to late diastolic filling from atrial contraction into a stiff ventricle.
S3 is linked to early diastolic rapid filling and is often discussed in volume overload states and systolic dysfunction (though clinical context matters).
Both can be low-frequency and better heard with the bell; tachycardia can blur distinction.
S4 vs murmurs
Murmurs are longer sounds caused by turbulent flow (often valvular stenosis/regurgitation or shunts).
S4 is brief and timed just before S1; it does not by itself define a valve lesion, though it may coexist with one (e.g., aortic stenosis).
Auscultation vs echocardiography
Auscultation is immediate and low-cost but subjective.
Echocardiography provides direct assessment of LVH, valve disease, ventricular function, and diastolic indices, and is typically used to confirm suspected structural disease.
Auscultation vs point-of-care ultrasound (POCUS)
POCUS may rapidly assess gross ventricular function and volume status in some settings.
It does not “replace” careful auscultation but can complement it; capability varies by device, training, and institution.
Observation/monitoring vs immediate testing
In low-risk presentations, clinicians may monitor and reassess rather than order immediate advanced testing.
In higher-risk contexts (e.g., concerning symptoms, abnormal vitals, suspected significant valve disease), more prompt diagnostic workup is commonly pursued; approaches vary by clinician and case.

S4 Common questions (FAQ)

Q: Where in the cardiac cycle does S4 occur?
S4 occurs in late diastole, immediately before S1. It aligns with atrial contraction (“atrial kick”) pushing blood into the ventricle. Clinically, it is often described with the cadence “ta-LUB-dub.”

Q: What does an S4 suggest physiologically?
S4 suggests reduced ventricular compliance, meaning the ventricle is relatively stiff during filling. This can be seen with LVH from hypertension, aortic stenosis, hypertrophic cardiomyopathy, and other processes that affect relaxation and compliance. It is a clue, not a standalone diagnosis.

Q: Can you hear S4 in atrial fibrillation?
A true S4 requires coordinated atrial contraction. In atrial fibrillation, atrial contraction is ineffective and irregular, so a classic S4 is not expected. If a late diastolic sound is suspected in this setting, clinicians consider alternative explanations or reassess timing.

Q: Is hearing S4 painful or uncomfortable for the patient?
No. Detecting S4 is part of routine auscultation with a stethoscope and is not painful. The main challenge is interpretive—timing and distinguishing it from other sounds.

Q: Does detecting S4 require anesthesia or special preparation?
No anesthesia is involved. Basic preparation is simply positioning (often left lateral decubitus for left-sided sounds) and minimizing environmental noise. In some cases, breath-holding for a moment can help the examiner focus on cardiac sounds.

Q: What is the “cost” of evaluating S4?
Listening for S4 is part of the physical exam and does not have a separate procedural cost in many clinical contexts. If S4 prompts additional tests (such as ECG or echocardiography), costs vary by healthcare system, insurer, device, and institution.

Q: How long does an S4 last once it appears?
S4 can persist as long as the underlying physiology (reduced compliance with effective atrial contraction) persists. It may vary day to day with heart rate, blood pressure, ischemia, or volume status. If the rhythm changes to atrial fibrillation, a true S4 typically disappears.

Q: Is S4 “dangerous” by itself?
S4 is not dangerous as a sound; it is a sign that may reflect underlying cardiac disease. The clinical importance depends on the cause (for example, severe aortic stenosis versus mild hypertensive LVH) and the patient’s symptoms and overall risk profile. Interpretation should be integrated with objective testing when indicated.

Q: Are there activity restrictions after an S4 is found?
S4 detection alone does not define activity limits. Activity guidance depends on the underlying diagnosis, symptom burden, and test results, and varies by clinician and case. Many patients require further evaluation before any disease-specific recommendations are made.

Q: How often should S4 be rechecked or monitored?
There is no universal interval for monitoring S4 specifically. Clinicians typically reassess heart sounds during routine follow-up visits, especially when managing hypertension, heart failure symptoms, or valvular disease. Imaging and objective measures usually drive monitoring schedules more than auscultation alone.