A heart murmur is an extra sound, often described as a whooshing or swishing noise, that a doctor hears through a stethoscope during a heartbeat. It’s caused by turbulent blood flow inside the heart or nearby blood vessels. Most murmurs are harmless, especially in children. An estimated 66% of all children will have a heart murmur detected at some point during childhood, and the vast majority of those require no treatment at all.
How a Murmur Is Produced
Blood normally flows through your heart and arteries in smooth, orderly streams. When something disrupts that smooth flow and makes it turbulent, the swirling blood creates pressure fluctuations that vibrate the walls of your heart or blood vessels. Those vibrations produce the sound your doctor picks up with a stethoscope. Research published in Circulation Research confirmed that turbulent flow is specifically what generates these sounds: when turbulence was absent, so was the murmur sound.
Think of it like water running through a garden hose. A smooth, open hose is nearly silent. Pinch the hose or put a kink in it, and you hear a rushing noise. The same principle applies inside your heart. A narrowed valve, a small hole, or simply faster-than-usual blood flow can all create that turbulence.
Innocent vs. Abnormal Murmurs
Doctors divide murmurs into two broad categories: innocent (also called harmless or functional) and abnormal (also called pathological). The distinction matters because they have very different implications.
Innocent murmurs occur in a structurally normal heart. They simply reflect blood moving a little faster or more forcefully than usual. Several temporary conditions can trigger one:
- Fever, which speeds up blood flow
- Anemia, where a lack of red blood cells forces the heart to pump harder
- Pregnancy, when blood volume increases significantly
- An overactive thyroid, which revs up the cardiovascular system
- Exercise or physical activity
- Rapid growth phases, like adolescence
These murmurs typically occur while the heart is contracting (called systolic murmurs), tend to be soft, and often disappear once the triggering condition resolves. A child with a fever might have a murmur one week and none the next.
Abnormal murmurs point to a structural problem in the heart, either something present since birth or something that developed over time. They tend to be louder, may have a distinctive pattern (like a crescendo that suddenly stops), and can occur during the relaxation phase of the heartbeat as well as during contraction. A murmur heard while the heart relaxes (a diastolic murmur) is almost always considered abnormal and warrants further investigation.
What Causes an Abnormal Murmur
The most common structural causes involve the heart’s four valves, which open and close with each heartbeat to keep blood flowing in one direction.
Stenosis happens when valve tissue stiffens and the valve opening narrows. The heart has to pump harder to push blood through the smaller opening, creating turbulence. Mild narrowing might not cause any noticeable problems, but severe stenosis forces the heart to work significantly harder and can strain the muscle over time.
Regurgitation (sometimes called a “leaky valve”) occurs when a valve doesn’t close completely, allowing blood to flow backward. The heart compensates by pumping harder, and the backward flow itself creates the turbulent sound. Over time, this extra workload can weaken the heart if left untreated.
Other causes include holes between heart chambers (septal defects), which are present from birth, and the natural hardening and narrowing of valves that can happen with aging.
How Murmurs Are Graded
Doctors rate murmur intensity on a scale of 1 to 6, sometimes written as fractions (like III/VI). The scale gives a quick shorthand for how prominent the sound is:
- Grade 1: Barely audible, even with a stethoscope
- Grade 2: Faint but clearly heard
- Grade 3: Loud, but no vibration felt on the chest
- Grade 4: Loud, with a vibration (called a “thrill”) that can be felt by pressing a hand on the chest
- Grade 5: Very loud, heard with a stethoscope barely touching the skin
- Grade 6: So loud it can be heard without a stethoscope
A higher grade doesn’t automatically mean a more dangerous condition. Some innocent murmurs can be moderately loud, and some serious valve problems produce quieter sounds. The grade is one piece of the puzzle, not the whole picture. Doctors also pay attention to where on the chest the murmur is loudest, when during the heartbeat it occurs, and how the sound pattern behaves.
Symptoms That Suggest a Problem
Many people with heart murmurs, even abnormal ones, feel perfectly fine. The murmur itself doesn’t cause symptoms. When symptoms do appear, they come from the underlying heart condition causing the murmur. Signs that a murmur may reflect something more serious include shortness of breath (especially with activity or when lying flat), persistent fatigue, swelling in the legs or abdomen, dizziness or fainting, and a bluish tint to the skin or fingertips. In infants, poor feeding and failure to gain weight can be warning signs.
How Murmurs Are Evaluated
The first step is always a physical exam. An experienced doctor can learn a lot just from listening: the location, timing, loudness, and pitch of the sound all provide clues. If the murmur has characteristics that suggest it’s innocent, especially in an otherwise healthy child, no further testing may be needed.
When a murmur raises concern, the primary tool for investigation is an echocardiogram, which is essentially an ultrasound of the heart. It produces a real-time image showing the heart’s valves, chambers, and blood flow patterns. This test can reveal whether a valve is narrowed or leaking, whether there’s a hole between chambers, and how well the heart is pumping overall. It’s painless, takes roughly 30 to 60 minutes, and involves no radiation.
Treatment and Monitoring
Innocent murmurs need no treatment. They aren’t a sign of disease and don’t limit your activities in any way.
For abnormal murmurs caused by valve disease, the approach depends on how severe the problem is and whether it’s causing symptoms or straining the heart. Mild to moderate valve issues are typically managed with periodic check-ups and repeat echocardiograms to track any changes over time. The goal of this monitoring is to catch progression before it causes irreversible damage to the heart muscle or puts excessive pressure on the lungs.
When valve disease becomes severe, particularly if symptoms develop or the heart begins to show signs of strain, intervention may be recommended. Options include surgical valve repair or replacement, and in some cases, less invasive catheter-based procedures that can fix a leaking valve without open-heart surgery. The purpose of these interventions is to relieve symptoms, prevent complications like heart failure or irregular heart rhythms, and extend life. The specific timing and approach depend on which valve is affected, how severe the damage is, and the patient’s overall health.
For murmurs caused by temporary conditions like anemia or an overactive thyroid, treating the underlying condition resolves the murmur. Once iron levels normalize or thyroid function is controlled, the extra turbulence disappears and the sound goes away.