A heart murmur is an extra sound heard through a stethoscope when blood flows through the heart in a turbulent, choppy way instead of smoothly. In most children, this is completely harmless. Up to 72% of children will have a murmur detected at some point during childhood or adolescence, and the vast majority of these are “innocent” murmurs with no connection to heart disease.
If your child’s doctor just mentioned a heart murmur at a routine checkup, there’s a good chance it falls into this normal category. But understanding the difference between an innocent murmur and one that signals a structural problem can help you know what to watch for.
What an Innocent Murmur Sounds Like
Innocent murmurs are extra heart sounds produced by blood flowing normally through a healthy heart. They don’t mean anything is wrong with the heart’s structure or function. The most common type in children is called a Still’s murmur, which has a distinctive low-pitched, musical quality almost like a humming vibration. It’s most often heard in children between ages 3 and 6, and the sound comes from the lower-left area of the breastbone.
A few things can make an innocent murmur louder or more noticeable. When your child is lying flat on their back, the murmur tends to be at its loudest, then gets softer when they sit or stand. Fever, excitement, and physical activity can also temporarily amplify the sound because the heart is pumping faster and pushing more blood with each beat. This is why a murmur sometimes shows up during a sick visit but wasn’t mentioned at the last well-child checkup. The murmur can come and go at different times, which itself is a reassuring sign.
Some innocent murmurs fade as children grow. Others stick around into adulthood without ever causing a problem. Either way, an innocent murmur doesn’t require treatment or activity restrictions. Your child can play sports, run around, and live without limitations.
When a Murmur Signals a Heart Problem
A small percentage of murmurs are “pathologic,” meaning they’re caused by a structural issue in the heart. These typically involve either a hole between heart chambers or a problem with one of the heart’s valves.
Holes between the lower chambers of the heart (ventricular septal defects) are one of the most common causes. Blood leaks through the opening with each heartbeat, creating a distinct whooshing sound that lasts through the entire contraction phase. Narrowed valves, where blood has to squeeze through a tighter opening than normal, can also produce murmurs. This narrowing can affect the valve leading to the lungs or the valve leading to the body’s main artery.
One useful rule: murmurs heard while the heart is relaxing and filling with blood (diastolic murmurs) are always considered abnormal and indicate a valve problem. Murmurs heard during contraction (systolic murmurs) can be either innocent or pathologic, so the sound’s timing alone isn’t enough to tell them apart. Your child’s doctor listens for specific characteristics like pitch, location, loudness, and how the sound changes with position to distinguish one from the other.
How Doctors Grade Murmur Intensity
Doctors rate murmurs on a scale from 1 to 6 based on how loud they are through the stethoscope. A grade 1 murmur is the faintest sound that can be reliably identified. Grade 2 is slight, grade 3 is moderate. At grade 4, the murmur is loud enough that the doctor can feel a vibration (called a thrill) on the chest wall with their hand. Grade 5 is very loud, and grade 6 can actually be heard with the stethoscope lifted just off the skin.
Innocent murmurs are typically soft, falling in the grade 1 to 2 range. A louder murmur doesn’t automatically mean something is wrong, but murmurs at grade 3 or above get more scrutiny. The grade helps your child’s doctor decide whether further testing is needed.
Symptoms That Suggest Something More Serious
An innocent murmur causes no symptoms at all. If a murmur is tied to a structural heart problem, your child may show signs that the heart isn’t pumping efficiently. In babies, this often looks like poor feeding, slow weight gain, fast breathing, or sweating during feedings. In older children, the signs can include getting unusually tired during exercise, chest pain, dizziness, or fainting.
Bluish color in the lips, fingertips, or feet is a particularly important signal. This means oxygen levels in the blood are lower than they should be, which can happen when blood flow through the heart isn’t following its normal path. Swelling in the legs, ankles, or belly can also point to the heart struggling to keep up with the body’s demands.
What Happens During Evaluation
Most innocent murmurs are diagnosed by a pediatrician during a physical exam based on the sound alone. If the murmur has characteristics that raise concern, or if your child has any of the symptoms described above, the next step is usually a referral to a pediatric cardiologist. Heart murmurs are actually the most common reason children get referred to a cardiologist.
The key test is an echocardiogram, which is essentially an ultrasound of the heart. It’s painless, uses no radiation, and gives doctors a detailed picture of the heart’s chambers, valves, and blood flow patterns. An echocardiogram is considered appropriate when a murmur is accompanied by abnormal signs or symptoms, when the murmur itself sounds pathologic on exam, or when there’s a family history of heart muscle disease or sudden unexplained death before age 50. An electrocardiogram (EKG), which records the heart’s electrical activity through stickers placed on the skin, may also be done.
For murmurs that sound clearly innocent in a child with no symptoms and no concerning family history, imaging isn’t necessary. Your pediatrician will simply continue to listen at future checkups and note any changes.
Outlook for Children With Murmurs
For the majority of children, a heart murmur is a normal finding that requires no treatment and carries no long-term consequences. Many innocent murmurs become quieter or disappear entirely as kids grow, though some persist into adulthood without causing issues.
When a murmur does turn out to be caused by a structural defect, the outlook depends entirely on the specific problem and its severity. Some small holes between heart chambers close on their own over time. Others may need monitoring or, in some cases, a procedure to repair. Valve problems range from mild (needing only periodic follow-up) to severe enough to require intervention. The echocardiogram gives doctors the information they need to determine which category your child falls into and how closely to follow them going forward.