What is a heart murmur?
Heart murmurs are extra, unusual sounds heard during a heartbeat — but why do they happen?
When a doctor listens to someone's heartbeat, they typically hear a characteristic sound: "lub-dub, lub-dub." In some people, though, this two-tone heartbeat is accompanied by whooshing or rasping noises, and these unusual sounds are called a heart murmur.
But what is a heart murmur, exactly, and what causes it?
A heart murmur indicates turbulent blood flow through the heart's valves, Dr. Kenneth Ellenbogen, a professor of cardiology and the director of clinical cardiac electrophysiology and pacing at the Virginia Commonwealth University School of Medicine, told Live Science by email.
"Murmurs may be benign and not indicate significant heart disease or may signify a valve problem requiring further evaluation and/or treatment," he said.
Related: What is a normal heart rate?
The typical "lub" and "dub" sounds of heartbeats are caused by different heart valves flapping shut as the heart muscle contracts.
Blood is pumped from the left and right atria, the chambers that receive blood from veins, to the left and right ventricles, which pump blood out to the body through arteries. Valves located between each atria-ventricle pair close to prevent the backflow of blood. This valve closure makes the "lub" sound.
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After the blood leaves the ventricles, the valves that separate the heart from arteries close, generating the "dub" sound. When this blood flow is disrupted, the classic lub-dub can be accompanied by the whooshing, humming or rasping sounds that are characteristic of heart murmurs, and these noises can be detected when a doctor listens to the heart through a stethoscope.
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Heart murmurs can be caused by an abnormal structure in the heart, such as a valve abnormality. For example, they may emerge when a valve doesn't close tightly enough, allowing blood to flow backward, or they might reflect a narrow or stiff valve.
Murmurs can also stem from a hole in the heart or a "cardiac shunt," meaning an irregular pattern of blood flow caused by a heart defect present at birth, Ellenbogen said. In addition, certain infectious diseases — such as bacterial endocarditis (an infection of the heart's lining) and rheumatic fever — can damage the heart and lead to heart murmurs, according to Yale Medicine.
Heart murmurs that are not caused by structural abnormalities or diseases of the heart are referred to as "innocent" or "physiological." These result from a marked increase in blood flow through the ventricles, Ellenbogen said.
Innocent heart murmurs are often diagnosed in babies and young people going through growth spurts, because to keep up with the body's rapid increase in weight and height, blood needs to flow more rapidly. Innocent heart murmurs are relatively common: about 10% of adults and 30% of children ages 3 to 7 experience them, according to Harvard Health.
Related: What's the rarest blood type?
Such benign heart murmurs are also common in pregnancy. During gestation, pregnant people's blood volume increases in order to nourish the growing fetus. This can change the heart's sounds, particularly between weeks 12 to 20 of pregnancy, but these murmurs are typically harmless.
An overactive thyroid, untreated high blood pressure and heart-rate-raising exercise may also cause heart murmurs, according to the British Heart Foundation.
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People with innocent heart murmurs don't tend to experience any symptoms. "Abnormal" heart murmurs — those tied to structural differences or heart disease — do not always cause symptoms but can be associated with trouble breathing, sweating, chest pain, weight gain, bulging neck veins and chronic cough. In babies and young children, symptoms of abnormal heart murmurs can also include feeding problems, poor growth and excessive fussiness, according to Yale Medicine.
Common risk factors for heart murmurs include intravenous drug use and family history of cardiac defects, according to Yale Medicine. Ellenbogen also noted that a person's existing heart murmur will become louder if they have a fever or anemia, meaning they have a deficiency in red blood cells or oxygen-carrying hemoglobin. That's because increased body temperature and low red blood cell count can affect the thickness of the blood, forcing the heart to pump blood faster, according to the medical resource StatPearls.
This article is for informational purposes only and is not meant to offer medical advice.
Anna Gora is a health writer at Live Science, having previously worked across Coach, Fit&Well, T3, TechRadar and Tom's Guide. She is a certified personal trainer, nutritionist and health coach with nearly 10 years of professional experience. Anna holds a Bachelor's degree in Nutrition from the Warsaw University of Life Sciences, a Master’s degree in Nutrition, Physical Activity & Public Health from the University of Bristol, as well as various health coaching certificates. She is passionate about empowering people to live a healthy lifestyle and promoting the benefits of a plant-based diet.