Innocent Heart Murmurs in Children: What They Mean

Innocent Heart Murmurs in Children: What They Mean

Your child is at a routine checkup, the stethoscope moves across the chest, and the clinician pauses and says, “I hear a murmur.” For most parents, that sentence lands hard. Here is what a murmur actually is, why most of them in children are completely harmless, and what makes a clinician want to look further.

What a murmur actually is

A heart murmur is a sound, not a diagnosis. Blood moving through the heart and the large vessels makes noise. Usually that noise is quiet enough that a stethoscope only picks up the two familiar beats — the “lub-dub” of the valves closing. A murmur is extra sound layered between or over those beats, made by blood moving quickly, or swirling, or passing through a narrower space than usual.

That extra sound can come from a structural problem with the heart. It can also come from a perfectly normal heart that simply happens to be small, thin-walled, and close to the chest wall — which describes most children.

When a murmur comes from a normal heart with normal structure and normal function, it is called an innocent murmur. You may also hear the terms functional murmur, physiologic murmur, or benign murmur. They all mean the same thing: the sound is real, the heart is fine.

How common are they

Very. Depending on the study and the age group, somewhere between a third and three-quarters of all children will have a murmur heard at some point during childhood. The great majority of those are innocent. Structural congenital heart disease, by contrast, affects roughly 1 in 100 births, and most significant cases are picked up in the newborn period or early infancy — often before a murmur is ever heard, through newborn pulse oximetry screening and the newborn exam.

So the base rates matter here. A murmur newly heard in an otherwise healthy, growing, active five-year-old is far more likely to be innocent than not.

Innocent murmurs also come and go. They tend to get louder when a child has a fever, is anemic, is anxious, or has just been running around, because blood is moving faster. A murmur heard clearly during a sick visit with a 102-degree fever may be entirely gone at the follow-up two weeks later. That is expected behavior for an innocent murmur, not a sign that something was missed.

How a clinician tells the difference

Most of the work happens with a stethoscope, a careful history, and hands on the child — not with technology. Experienced pediatric examiners are quite good at this.

The features that point toward an innocent murmur include:

• Timing. Innocent murmurs are systolic, meaning they occur during the part of the beat when the heart is squeezing. They are also usually short rather than filling the whole phase.
• Softness. Innocent murmurs are typically grade 1 or 2 out of 6 — quiet, sometimes only audible in a silent room.
• Quality. Many have a distinctive musical, vibratory, or humming character. The classic Still’s murmur, the most common innocent murmur in school-age children, sounds almost like a plucked string.
• Position change. Innocent murmurs often get noticeably quieter or vanish when the child sits up or stands, and get louder lying down.
• Everything else is normal. Normal growth, normal pulses in the arms and legs, no thrill (a vibration you can feel), normal heart sounds otherwise, no signs of heart strain.

There are several named innocent murmurs beyond Still’s — the pulmonary flow murmur of adolescence, the venous hum in the neck, peripheral pulmonary stenosis in young infants, and the supraclavicular bruit. Each has a recognizable pattern.

Features that prompt a closer look

Some findings shift the balance and lead a clinician to order further testing or refer to pediatric cardiology. These include:

• A diastolic murmur — sound occurring during the relaxation phase. Diastolic murmurs are essentially never innocent and always warrant evaluation.
• A loud murmur, grade 3 or above, or any murmur with a palpable thrill.
• A harsh or blowing quality, or a murmur that continues through both phases of the beat.
• Abnormal or unequal pulses, especially weak or delayed femoral pulses in the groin compared with the arms, or a significant blood pressure difference between arms and legs.
• Symptoms. Poor weight gain or feeding difficulty in an infant. Exercise intolerance that is out of proportion to peers. Chest pain with exertion. Fainting during exercise — as opposed to fainting after standing still in a hot room, which is usually benign. Palpitations. Blue or dusky color around the lips.
• An abnormal second heart sound, a click, or a gallop.
• Family history of sudden cardiac death under age 50, unexplained drowning or car accident in a young relative, cardiomyopathy, long QT syndrome, or Marfan syndrome.
• Certain genetic conditions known to carry higher rates of heart defects, such as Down syndrome or 22q11 deletion.

It is worth saying plainly: none of these findings means something is definitely wrong. They mean the sound has not been fully explained yet, and it is worth explaining.

What an echocardiogram involves

If further evaluation is recommended, the main test is an echocardiogram — an ultrasound of the heart. It is worth knowing what it is and is not.

An echocardiogram uses sound waves, the same technology as a pregnancy ultrasound. There is no radiation. There are no needles. It does not hurt. A technician puts warm gel on the chest and moves a probe around while pictures of the heart’s chambers, valves, and blood flow appear on a screen. It usually takes somewhere between 20 and 45 minutes.

For older children, it is mostly a matter of holding still and being a little bored. For toddlers, who are the least cooperative age group for lying flat, a tablet or a favorite show usually does the job. Very young or very anxious children occasionally need sedation, but this is uncommon for a straightforward murmur evaluation.

An EKG, which records the heart’s electrical activity through stickers on the skin, is sometimes done alongside it. It takes a couple of minutes.

If you are told your child needs an echocardiogram, that is not a signal that the clinician suspects something serious. Often it is the opposite — it is a way to close the question definitively so nobody has to wonder again.

What an innocent murmur means for daily life

Nothing. That is the honest answer, and it is worth stating without hedging.

A child with an innocent murmur has a structurally normal heart. There are no activity restrictions. No sports limitations. No need to sit out gym class, avoid competitive teams, or skip travel soccer. No antibiotics before dental work. No special diet. No cardiology follow-up in most cases. No effect on life insurance or future health.

The murmur will usually fade during adolescence as the chest wall thickens and the heart sits further from the stethoscope. Some persist quietly into adulthood and still mean nothing.

One practical note: because innocent murmurs are common and clinicians rotate, your child may get “I hear a murmur” again from a different provider at a sports physical or an urgent care visit. Keeping a note in your phone — the date the murmur was evaluated, whether an echocardiogram was done, and the result — saves a lot of repeated worry.

About the anxiety

The word murmur carries weight that the finding usually does not deserve. It sounds like something is wrong with the heart, and the heart is the organ parents worry about most.

If you leave a visit unsettled, say so. Ask directly: do you think this is innocent, and what would change your mind? A clear answer in the room is worth more than an evening of searching online. And if the plan is watchful waiting, ask what specifically you should watch for.

Murmurs are a standard part of what gets listened for at every well-child visit, which is one of the reasons those visits stay on the schedule even in years when nothing seems to be going on. Most are found there, and most are found to be nothing.

Call 911 if your child collapses, faints during exercise, has trouble breathing, or turns blue around the lips.

Talk with us

If a murmur has been mentioned at a checkup, a school physical, or an urgent care visit, bring it up at your child’s next appointment so it can be sorted out properly. You can book a visit or get in touch with any questions about what was heard and what happens next.