A heart murmur is an atypical heart sound due to rapid, turbulent blood flow through the heart. Murmurs can be innocent or abnormal. While an innocent murmur can resolve without treatment, an abnormal murmur indicates an underlying health condition.

Without a murmur, the blood flows through the heart smoothly and quietly. A regular heartbeat makes a “lub-dub, lub-dub” sound.

In the case of a murmur, the heart makes an extra, atypical sound as the heart beats. This happens as the blood flows turbulently rather than smoothly through the blood vessels, causing adjacent soft-cardiac tissues to vibrate.

This article explores heart murmur sounds. It also discusses the types, causes, and outlook of heart murmurs.

A doctor listening to a person's heart to identify heart murmurs.Share on Pinterest
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The heart consists of four valves and four chambers. The left and right atria make up the two upper chambers, and the lower chambers consist of the left and right ventricles.

Heart sounds happen as the blood flows through the chambers of the heart as the valves open and close.

In a healthy adult, the heart makes a “lub-dub” sound. This happens as blood flows through the heart chambers and cardiac muscles contract and relax during each cardiac cycle.

The types of heart sounds include the:

  • S1: The first heart sound, “lub” or S1, is due to vibrations from the closure of the mitral and tricuspid valves, or atrioventricular valves. It occurs after the atria pump blood into the ventricles. The closure of the mitral valve is the louder component of S1.
  • S2: The second heart sound, “dub” or S2, represents the closure of the aortic and pulmonary valves right after the ventricles eject blood into the aorta and pulmonary artery. Between S1 and the next S2, the ventricles contract, which doctors call systole. Between S2 and the next S1, the ventricles relax, which doctors call diastole.
  • S3: The S3, or ventricular gallop, is a low-pitched heart sound that can occur immediately after the typical “lub-dub, lub-dub” heart sound. Healthcare professionals believe the sound occurs when oxygenated blood gushes rapidly from the atrium, passes through the mitral valve, and hits the walls of an over-filled left ventricle. Healthy children, pregnant people, and well-trained athletes may have S3. An S3 can sometimes also indicate an underlying heart condition such as heart failure.
  • S4: The fourth heart sound, S4, or atrial gallop, occurs during late diastole before the heart makes the usual “lub-dub, lub-dub” heart sound. The heart produces this turbulent sound when the atria contract to forcefully pump blood into a stiff or less compliant left ventricle.

Learn more about heart sounds.

According to the American Heart Association (AHA), there are two types of heart murmurs — innocent and abnormal.

Innocent heart murmurs are harmless and can occur in a healthy heart.

During an innocent heart murmur, the heart beats typically but makes extra sounds as blood flows through the heart. The sound may be similar to air moving through an air duct.

They are usually common in children. An innocent heart murmur may become louder or softer during excitement, fear, or a temperature change.

The video below from Khan Academy shows the different types of heart sounds that relate to heart murmurs:

Abnormal heart murmurs can develop due to problems with the heart valves.

The types of abnormal heart murmur include:

Systolic murmur

A systolic murmur begins during the first heart sound and ends before the second heart sound.

The doctor can hear a “swish” sound after the atrioventricular valve closes while the ventricles are pumping blood to the lungs and body.

Diastolic murmur

A diastolic murmur is an unusual “whoosh” sound in the heart that occurs during the period after S2 and before S1.

The heart produces a diastolic murmur as the ventricles relax and fill with blood.

Continuous murmur

A continuous murmur occurs throughout a cardiac cycle as the heart contracts and relaxes.

They can be intense, rough, and come with a trembling “hum” sound.

Continuous murmurs can be observable in people with patent ductus arteriosus, a congenital heart abnormality.

There are two typical heart sounds in a healthy adult.

The first heart sound, or “lub,” is a low-pitched, dull sound that occurs from closing the mitral and tricuspid valves when blood flows from the atria to the ventricles.

The second heart sound, or “dub,” indicates the closing of the semilunar valves as the ventricles eject blood.

The video below from Khan Academy shows the typical sounds a heart makes:

A heart murmur is an audible-vibrational whooshing, humming, rasping, or swishing sound due to turbulent blood flow.

A heart murmur is different from a typical heart sound. If a doctor hears a sound that is concerning for an atypical heart murmur, they will order additional testing.

According to the British Heart Foundation (BHF), most heart murmurs are harmless. However, they can indicate an underlying heart condition, such as a heart valve disease or a congenital heart abnormality.

According to a 2021 article, a heart murmur is the most common reason healthcare practitioners refer children to pediatric cardiologists for evaluation. The article adds that 72% of children experience a heart murmur at some point in their lives.

Usually, benign murmurs will go away with age. However, on rare occasions, some children may live with a heart murmur into adulthood.

Learn more about heart murmurs.

The BHF states that innocent heart murmurs can occur as a result of:

Innocent heart murmurs in children and babies can happen as a result of rapid growth spurts.

Abnormal heart murmurs develop due to a problem with the heart, such as an infection, congenital heart condition, or heart valve disease.

Some causes of an atypical heart murmur can include:

  • Endocarditis: Germs or infections can travel from another part of the body and lodge in the damaged areas of the heart. Without treatment, endocarditis can affect the heart and cause a heart murmur.
  • Heart valve disease: The heart consists of four valves that keep blood flowing in the right direction. A damaged heart valve can disrupt blood flow across the heart resulting in a heart murmur. The valves can be narrow (stenotic) or leaky (regurgitant), and in either case, these can result in a heart murmur.
  • Chronic rheumatic heart disease: One or more episodes of rheumatic fever can damage the heart valves, leading to a heart murmur. They can also increase a person’s risk of blood clots and stroke.
  • Congenital heart defects: A person with a congenital heart abnormality has issues in the structures of their heart from birth. This abnormality can affect the functions of the heart valves, resulting in a heart murmur. Atypical connections in the heart and blood vessels can also cause murmurs.

If a person has a heart murmur, they should contact a doctor. The doctor will evaluate a person’s symptoms and determine the cause.

An innocent heart murmur will not require medication. In some cases, the murmur will disappear as a child reaches adulthood.

The outlook for atypical heart murmurs will depend on the cause. Depending on the underlying reason, the doctor may recommend surgery to repair a heart valve abnormality. Others may be able to lead a typical life without surgery.

A heart murmur can be asymptomatic. This means that many people with the condition may not feel any symptoms.

However, a person should contact a doctor right away if they have any of the following symptoms:

The doctor will listen to a person’s heart sounds and order additional tests.

A heart murmur is an extra, unusual sound that occurs from turbulent blood flowing through the heart. It can make a whooshing, rasping, or humming sound similar to air passing through an air duct.

A murmur can be benign or atypical. While benign murmurs resolve naturally, atypical murmurs suggest an underlying health condition.

Many people with the condition may not know because it can be asymptomatic. If a person suspects they have a heart murmur, they should contact a doctor as soon as possible.