Most heart murmurs are not dangerous. A heart murmur is simply an extra sound that blood makes as it flows through the heart, and the majority are harmless, especially in children. These “innocent” murmurs require no treatment and often disappear on their own. A smaller number of murmurs, however, signal a structural problem with the heart that needs attention. The difference between a harmless murmur and a worrisome one comes down to its characteristics, whether symptoms are present, and what’s causing it.
What an Innocent Murmur Sounds Like
Innocent murmurs, also called flow murmurs or functional murmurs, are extremely common. They happen when blood flows through a healthy heart with enough turbulence to create an audible whooshing sound. Children are especially prone to them because their chest walls are thinner and their hearts sit closer to the stethoscope.
Doctors recognize innocent murmurs by a set of features sometimes called the “seven S’s”: they’re soft, short in duration, heard over a small area of the chest, occur only during the pumping phase of the heartbeat, produce a single sound without clicks or snaps, have a smooth (not harsh) quality, and change with position or breathing. In children two and older, if a murmur completely disappears when the child stands up, there’s a 98% chance it’s innocent.
Innocent murmurs don’t cause symptoms. They don’t weaken the heart, they don’t get worse over time, and they don’t need treatment. Many children outgrow them entirely.
When a Murmur Points to a Problem
A pathological murmur is caused by a structural issue in the heart, such as a valve that doesn’t open or close properly, a hole between heart chambers, or thickened heart muscle. These murmurs tend to sound different from innocent ones. They’re often louder, harsher, last longer through the heartbeat, or radiate to the back or neck. Some occur during the filling phase of the heartbeat (diastolic murmurs), which is almost never innocent.
Doctors grade murmur loudness on a scale of 1 to 6. Grade 1 and 2 murmurs are faint and commonly turn out to be functional, often linked to temporary causes like fever, anemia, or a fast heart rate. They frequently disappear once those conditions resolve. Grade 3 and above, though, are louder and more strongly associated with actual heart disease. That said, a loud murmur doesn’t automatically mean a severe problem. Some structural defects cause dramatic sounds but carry a relatively good prognosis.
If a doctor can feel a vibration (called a thrill) on the chest wall while listening, or if the chest visibly lifts with each heartbeat, a structural heart problem is likely.
Symptoms That Signal Something Serious
An innocent murmur produces no symptoms at all. When a murmur is tied to an underlying heart condition, the symptoms come from the condition itself, not the sound. Watch for:
- Shortness of breath during normal activity or at rest
- Chest pain
- Fainting or dizziness, especially during exercise
- Blue or gray tint to the fingernails, lips, or skin
- Swelling in the legs, ankles, or abdomen, or sudden unexplained weight gain
- Swollen neck veins
- Heavy sweating with little or no physical effort
- A persistent cough that doesn’t go away
- In infants, poor feeding and failure to gain weight
Any of these alongside a known murmur is a reason to get evaluated promptly. The symptoms often point to a valve problem, a hole in the heart wall, or heart muscle disease that’s forcing the heart to work harder than it should.
How Doctors Figure Out the Cause
A stethoscope exam gives your doctor the first clues: where the murmur is loudest, when it occurs in the heartbeat, how it changes when you shift position, and whether there are extra sounds like clicks. But listening alone can’t confirm a diagnosis.
The main test for pinpointing the cause of a murmur is an echocardiogram, an ultrasound of the heart. It creates a real-time picture of the heart’s chambers, valves, and blood flow, and it can show exactly whether a valve is leaking, narrowed, or structurally abnormal. The test is painless and takes about 30 to 60 minutes. An electrocardiogram (EKG) may also be done to check the heart’s electrical activity for signs of strain or rhythm problems. Together, these two tests give a clear picture of whether the murmur is something to treat or something to simply note and move on from.
Common Structural Causes
When a murmur does indicate a problem, the most frequent culprits in adults are valve diseases. Aortic stenosis means the valve controlling blood flow out of the heart has stiffened or narrowed, forcing the heart to pump harder. Mitral regurgitation means the valve between the left chambers doesn’t seal completely, allowing blood to leak backward. Both of these conditions can worsen over time if left untreated, eventually leading to heart failure, dangerous heart rhythms, or stroke.
In children, pathological murmurs are more often tied to congenital heart defects, meaning something formed differently before birth. Ventricular septal defects (a hole between the lower chambers) and atrial septal defects (a hole between the upper chambers) are among the most common. Small holes sometimes close on their own as a child grows. Larger ones may need a procedure to repair.
Murmurs During Pregnancy
Pregnancy is one of the most common triggers for a new, harmless murmur. Roughly 93% of pregnant women develop a detectable heart murmur at some point during pregnancy. This happens because blood volume increases significantly to support the growing baby, and the heart pumps faster and harder to keep up. The extra flow creates turbulence that a stethoscope can pick up.
These pregnancy-related murmurs don’t cause clinical problems. Most fade within about six weeks after delivery as blood volume returns to normal.
What Happens if a Pathological Murmur Goes Untreated
The murmur itself isn’t the threat. The danger lies in the underlying condition progressing without treatment. A narrowed or leaking valve, for example, puts extra strain on the heart muscle year after year. Over time, the heart can enlarge, weaken, and lose its ability to pump efficiently. This progression can lead to heart failure, where fluid backs up into the lungs and body, or to blood clots that increase the risk of stroke.
Damaged or abnormal valves also carry a higher risk of infective endocarditis, a serious infection of the heart’s inner lining. For these reasons, people with known valve disease typically need regular monitoring with echocardiograms, even if they feel fine, so that doctors can track any changes and intervene before the heart sustains permanent damage.
Who Needs Further Evaluation
Deciding whether a murmur needs further workup depends on three things: the sound’s characteristics, the presence of symptoms, and the patient’s overall health. A soft, short murmur in an otherwise healthy child with no symptoms is very likely innocent and may not need any testing beyond a physical exam. A harsh murmur in an adult with shortness of breath or dizziness is a different story entirely.
Children with murmurs that have any unusual features are typically referred to a pediatric cardiologist for an echocardiogram. Adults who develop a new murmur, especially those over 50 or those with risk factors like high blood pressure or a history of rheumatic fever, generally get an echocardiogram to rule out valve disease. If testing confirms the murmur is innocent, no follow-up is needed. If it reveals a structural problem, the treatment plan depends on what’s found and how severe it is, ranging from periodic monitoring to valve repair or replacement.