Still’s murmur is a harmless heart sound heard in otherwise healthy children, and it is the most common innocent murmur in pediatrics. First described by the British physician George F. Still in 1909, it has a distinctive musical or vibratory quality that sets it apart from both pathological murmurs and other types of innocent murmurs. Despite carrying zero risk of heart disease, a Still’s murmur is also one of the most common reasons children end up in a pediatric cardiologist’s office, largely because the sound can alarm parents and primary care providers who are unsure what they are hearing.
What a Still’s Murmur Sounds Like
The defining feature of a Still’s murmur is its musical, almost twanging quality. Clinicians often describe it as sounding like a vibrating string or a kazoo being played softly against the chest wall. It is low to medium pitched, confined to early systole (the phase when the heart contracts to pump blood), and generally quiet, graded around a 2 on the standard 1-to-6 loudness scale, though it can range from 1 to 3.1ScienceDirect. THE CARDIAC MURMUR: When to Refer? – Section: THE VIBRATORY STILL’S MURMUR The sound is best heard at the lower left edge of the breastbone and can extend toward the apex of the heart. It does not radiate widely across the chest, and it tends to get louder when a child is lying flat, has a fever, or is anxious or excited, because blood flow speeds up in those situations.
Phonocardiography, which records heart sounds as waveforms, reveals that the vibratory murmur has a strikingly uniform wave form at a constant frequency. This regularity persists even when the recording device is placed away from the point where the murmur sounds loudest.2ScienceDirect (American Heart Journal). Phonocardiographic differentiation of vibratory (functional) murmurs from those of valvular insufficiency That consistent, almost tonal character is what gives experienced listeners their confidence in the diagnosis. By contrast, murmurs caused by valve problems or holes between heart chambers tend to be harsher, higher-pitched, or blowing in quality, and their waveforms look far more chaotic on a phonocardiogram.
When It Appears and How Common It Is
Still’s murmur is most often heard in children between the ages of about two and six, though it can show up as early as infancy and linger into adolescence.3ScienceDirect. THE CARDIAC MURMUR: When to Refer? – Section: THE VIBRATORY STILL’S MURMUR In practical terms, nearly every child will have some kind of heart murmur detected at some point during childhood. Less than one percent of murmurs in children turn out to be pathological, and innocent or functional murmurs are by far the most common type.4PubMed Central. Innocent Heart Murmur Among those innocent murmurs, Still’s is the one pediatricians encounter most frequently.
The murmur often becomes noticeable during routine well-child checkups, or when a child visits the doctor with a fever or minor illness. Because fevers and dehydration increase the speed of blood moving through the heart, the murmur can sound louder than usual during those visits, which sometimes leads to a referral that might not have happened at a calm, healthy appointment. As children grow and their chest walls thicken, the murmur typically becomes harder to hear and eventually disappears, though the timeline varies from child to child.
What Causes the Sound
The honest answer is that researchers have debated this for decades and have not settled on a single explanation. The most discussed theory involves structures called left ventricular false tendons, which are thin, string-like bands of tissue stretching across the inside of the left ventricle. The idea is straightforward: blood flowing past these bands makes them vibrate, much like wind passing over a guitar string, producing the musical tone that defines Still’s murmur.
Some echocardiographic studies have found a strong association. One study found false tendons in a small fraction of pediatric patients, but among those without underlying heart disease, about 94% had a murmur of the Still’s type.5PubMed. Left ventricular false tendons in children: prevalence as detected by 2-dimensional echocardiography and clinical significance A separate investigation looking at how vibratory murmurs are generated reviewed similar data and noted an apparent link between false tendons and vibratory murmurs, though it also acknowledged that not all researchers agreed. One study found a much higher prevalence of false tendons (61%) in the general population but no correlation with any type of murmur.6The American Journal of Cardiology. Genesis of vibratory functional murmurs
A case-control study comparing schoolchildren with vibratory innocent murmurs to matched controls without murmurs found no significant difference in the prevalence of false tendons between the two groups, and also no meaningful differences in left ventricular size, function, or other cardiac measurements.7PubMed. The vibratory innocent heart murmur in schoolchildren: a case-control Doppler echocardiographic study So the false tendon theory has support in some data sets and not others, leaving the picture unresolved.
Other proposed explanations include turbulence at the aortic root, vibrations of the pulmonary valve leaflets, and flow patterns related to the geometry of the left ventricular outflow tract. None of these theories has definitively won out. What everyone does agree on is that whatever creates the sound, it reflects normal blood flow through a structurally normal heart. There is no damage, no leaking valve, and no hole.
How Doctors Distinguish It From Pathological Murmurs
An experienced clinician can often identify a Still’s murmur by listening alone, without any imaging. The key is that combination of qualities: musical or vibratory tone, low to medium pitch, soft intensity, location at the lower left sternal border, and confinement to early systole. Certain bedside maneuvers help confirm the diagnosis. Having the child sit up or stand often makes the murmur softer or causes it to disappear entirely, while lying down makes it louder. A Valsalva maneuver (bearing down as if straining) can reduce it. Pathological murmurs from conditions like ventricular septal defects or aortic stenosis behave differently with these position changes and tend to have harsher, more constant qualities.
Still’s murmur also needs to be distinguished from other innocent murmurs, because not all benign heart sounds in children are Still’s. A pulmonary flow murmur, for instance, is heard higher on the chest at the second or third interspace near the left sternal border. It has a crescendo-decrescendo shape and a rougher, more dissonant quality without the vibratory musicality of Still’s murmur. A venous hum, another common innocent sound in children, is continuous rather than just systolic and is best heard at the base of the neck. It disappears when the child lies down or when you gently compress the jugular vein on the same side.8ScienceDirect. THE CARDIAC MURMUR: When to Refer? – Section: THE PULMONARY FLOW MURMUR / The Venous Hum
The red flags that suggest a murmur might be pathological include a loud murmur (grade 3 or above), a diastolic murmur (heard during the heart’s relaxation phase rather than its contraction), a murmur with a harsh or blowing quality, radiation of the sound to the back or neck, an abnormal second heart sound, or any symptoms like poor feeding in infants, failure to gain weight, exercise intolerance, or cyanosis. If any of those features are present, echocardiography is warranted.
When an Echocardiogram Is Actually Needed
Heart murmurs are the single most common reason children get referred to a pediatric cardiologist, and a large portion of those referrals turn out to involve innocent murmurs.9PubMed Central. Innocent Heart Murmur The question of when to order an echocardiogram (an ultrasound of the heart) is a real tension in clinical practice. On one hand, the test is non-invasive and gives definitive reassurance. On the other hand, it costs money, uses specialist time, and can itself generate anxiety if incidental findings come up.
A study of over 1,700 children referred for murmurs found that about 31% received an echocardiogram. Among those whose echo was rated as appropriate by clinical criteria, abnormal findings were present in about 130 cases. Among those whose echo was rated as rarely appropriate, none had abnormal findings.10PubMed. Appropriate Use and Clinical Impact of Echocardiographic “Evaluation of Murmur” in Pediatric Patients – Section: RESULTS The takeaway is that when clinical features clearly suggest an innocent murmur, the echo rarely adds useful information. A skilled examiner who hears the classic Still’s murmur in an otherwise healthy, asymptomatic child with a normal exam can reassure the family without imaging.
That said, many primary care providers understandably feel more comfortable with a confirmed normal echo, especially when parental anxiety is high. Practice varies by region, insurance coverage, and how accessible pediatric cardiology services are. In settings where a pediatric cardiologist is not available, echocardiography serves as a safety net to make sure nothing has been missed.
Why an Innocent Murmur Diagnosis Can Still Raise Anxiety
Hearing the word “murmur” in connection with your child’s heart tends to be alarming, regardless of the reassurance that follows. Research on parental reactions has shown that nearly half of parents believe a heart murmur signifies actual heart disease or that it could interfere with their child’s ability to exercise. About a fifth of parents felt that their other children should also be tested even if those children had no murmur at all.11PubMed. Parental anxiety and misperceptions in children with innocent murmurs – Section: RESULTS
Perhaps counterintuitively, the same study found that parental anxiety scores actually increased after the cardiology consultation. Measured using a standardized anxiety questionnaire, the average score rose from about 17 before the visit to about 23 afterward.12PubMed. Parental anxiety and misperceptions in children with innocent murmurs – Section: RESULTS The likely explanation is that simply being in a cardiology office, surrounded by clinical language and the weight of a specialist visit, amplifies worry even when the outcome is reassuring. This finding suggests that how the diagnosis is communicated matters as much as the diagnosis itself. Some pediatric cardiologists have moved away from using the word “murmur” entirely when speaking with families, preferring phrases like “normal heart sound” or “innocent heart sound” to avoid the loaded connotations.
Children with innocent murmurs need no activity restrictions whatsoever. They can run, swim, play competitive sports, and do everything any other child does. There is no medication, no follow-up monitoring schedule, and no lifestyle change required. The murmur carries zero morbidity or mortality risk.13PubMed Central. Innocent Heart Murmur If a provider is recommending restrictions based on a murmur that has been identified as innocent, that warrants a conversation or a second opinion.
The Challenge of Auscultation Skill
One underappreciated issue is that identifying murmurs by ear is genuinely hard, even for trained physicians. A study enrolling 56 pediatric residents across different training levels found that their accuracy at correctly identifying murmur types on simulation mannequins hovered around 50 to 53%, and their accuracy at reaching the correct diagnosis was even lower, roughly 33 to 36%.14PubMed Central. Comparison of Cardiac Auscultation Features on Four Different Simulation Mannequins Performed by Pediatric Residents Seniority did not make a significant difference in these scores. This does not mean residents are poorly trained; it reflects how difficult auscultation is as a perceptual skill. Distinguishing a vibratory innocent murmur from a soft ventricular septal defect murmur requires experience that accumulates slowly over years of clinical practice.
This skill gap helps explain why so many children with innocent murmurs get referred onward. A primary care doctor who is not fully confident in what they are hearing will, correctly, err on the side of caution and send the child to a specialist or order an echocardiogram. The cost of missing a pathological murmur is much higher than the cost of an unnecessary referral. Still, the volume of referrals does place strain on pediatric cardiology services and can generate unnecessary anxiety for families.
Digital Stethoscopes and AI-Assisted Detection
Researchers have begun exploring whether artificial intelligence can bridge the auscultation skill gap. A recent multicenter study tested deep learning models trained to identify Still’s murmur from digital stethoscope recordings and distinguish it from both other innocent murmurs and pathological ones. The models achieved sensitivity between about 91% and 100%, specificity between 75% and 98%, and overall accuracy between roughly 91% and 99%.15PubMed Central. Advancing Point-of-Care Still’s Murmur Identification: Evaluating the Efficacy of ConvNets and Transformers Using the StethAid Multicenter Heart Sound Database – Section: IV. RESULTS
These are early-stage results and reflect research conditions rather than real-world clinics, but the direction is promising. If a digital stethoscope could reliably flag a murmur as “likely Still’s” during a routine office visit, primary care providers might feel more confident reassuring parents on the spot rather than referring. That could reduce unnecessary specialist visits, lower healthcare costs, and, perhaps most importantly, spare families the anxiety spiral that comes with a cardiology referral for a perfectly healthy child. Several companies are already developing and marketing digital stethoscopes with AI-assisted analysis, though regulatory clearance and real-world validation remain ongoing challenges.
Still’s Murmur in Adults
While Still’s murmur is overwhelmingly a pediatric finding, its disappearance during adolescence is not universal. Some adults continue to have a vibratory systolic murmur with the same acoustic profile. In adults, the clinical challenge shifts somewhat: the same low-pitched systolic murmur at the lower left sternal border could potentially be a still-innocent Still’s murmur, but it could also represent early aortic valve disease, hypertrophic cardiomyopathy, or other acquired conditions that become more relevant with age. Adults with this type of murmur are more likely to receive an echocardiogram simply because the pretest probability of structural heart disease increases over time.
In young, otherwise healthy adults with no symptoms, no family history of sudden cardiac death, and a classic vibratory murmur that responds to positional changes the way an innocent murmur should, the clinical reasoning is similar to pediatrics. But the threshold for imaging is generally lower in adults because the stakes of missing acquired valve disease are different. If you are an adult who has been told you have a murmur and you are unsure whether it has been properly evaluated, an echocardiogram is a reasonable and straightforward way to settle the question.
Other Innocent Murmurs That Get Confused With Still’s
Families sometimes come away from a visit thinking their child has “an innocent murmur” without realizing there are several distinct types, each with different locations and acoustic profiles. Understanding the landscape helps make sense of what the doctor heard.
- Pulmonary flow murmur: Heard higher on the chest than Still’s, near the second or third interspace along the left sternal border. It has a crescendo-decrescendo pattern and a rough quality rather than the musical tone of Still’s.
- Venous hum: A continuous, low-pitched murmur heard at the base of the neck, caused by blood flowing through the jugular veins. It is most audible when the child is sitting up and disappears when lying down or when the vein is gently compressed.
- Peripheral pulmonary stenosis murmur: Common in newborns, caused by the relatively sharp angle at which the pulmonary artery branches in small infants. It typically resolves within the first few months of life as the vessels grow.
Each of these is benign. The distinction matters mainly for the examining physician, who uses the sound characteristics and location to confirm that the murmur matches a recognized innocent pattern rather than something that needs further workup. For parents, the practical message is the same across all of them: if the doctor or cardiologist has confirmed the murmur is innocent, your child’s heart is normal and no treatment or monitoring is needed.