The S3 heart sound occurs as the mitral valve opens and allows blood to fill the left ventricle passively. The sound happens as a result of blood striking the left ventricle during early diastole.

An S3 heart sound can indicate heart failure in some people. However, doctors may also hear it in healthy individuals. Doctors typically listen to heart sounds by placing a stethoscope on the chest wall.

A healthy heart typically makes two sounds: as the heart valves open and close, and as blood rushes through the heart. The valves are responsible for controlling blood flow through the heart. The vibration of the structures in the heart creates the sounds — the more turbulent the blood flow, the more vibration and sound.

If blood rapidly rushes into an overfilled left ventricle, it creates the S3 heart sound.

Read on to learn more about the S3 heart sound and what can cause it.

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Heart sounds occur as blood flows through the heart chambers and as its valves open and close during a heartbeat.

Typically, a heart makes two sounds that people describe as “lub-dub.” Doctors refer to these as S1 and S2 sounds. Sometimes, the heart also makes third and fourth sounds, or S3 and S4.

The S3 heart sound occurs as the mitral valve — which sits between the left atrium and left ventricle — opens and allows blood to fill the left ventricle passively. The sound happens due to blood striking the left ventricle during early diastole. Early diastole refers to when the ventricle starts to expand and the pressure within it is low.

Doctors can most easily hear the sound at the cardiac apex. This is the pointed tip of the heart that lies to the left of the sternum, between the fourth and fifth ribs.

What does it indicate?

Some healthy people have S3 heart sounds. Doctors may find it in children, pregnant people, and well-trained athletes. However, it may also indicate heart problems such as systolic heart failure.

The third heart sound is an initial clue of heart failure that doctors associate with severe heart problems and death.

In some cases, S3 heart sounds may indicate a diastolic murmur. This is an unusual finding that may suggest valve issues within the organ. These valve issues include severe tricuspid or mitral valve regurgitation. Regurgitation means that the heart valve becomes leaky.

Learn more about common heart valve disorders here.

The S3 or third heart sound is a low-frequency, short vibration sound.

It happens after the S2 sound. Typically, the S2 is a high-pitched sound, which is how doctors can distinguish the low, dull S3 sound.

Doctors may also refer to the S3 sound as a ventricular gallop. This may be because the three heart sounds — S1, S2, and S3 — in quick succession create a cadence, or rhythm, like a galloping horse.

Additionally, the heart sounds follow a similar galloping rhythm to the cadence of the word “Kentucky.” Specifically, the last syllable, “cky,” represents the S3 sound.

However, doctors may find it challenging to detect the sound as it can be subtle.

The S3 sound can occur if an individual has congestive heart failure. In this situation, the heart cannot pump enough blood around the body to keep it healthy. As a result, blood does not move through the heart as it should, which may lead to an individual having S3 heart sounds.

Various conditions can lead to congestive heart failure, including uncontrolled high blood pressure, a sedentary lifestyle, high levels of blood fat, smoking, and diabetes.

People with conditions that lead to increased blood volume in the left atrium, increased ventricular filling pressure, or both, can experience S3 heart sounds.

Doctors remain unsure of the exact mechanisms for creating S3 heart sounds. Traditionally, they assumed that blood rushing into an overloaded ventricle caused the sound, for example, during an exacerbation of acute heart failure.

However, more recent research suggests that the diameter of the mitral valve annulus — the junction between the ventricle and left atrium — is important in S3 sound creation.

Doctors may refer to the fourth heart sound, or S4, as atrial gallop. It occurs as the atria push blood into a stiff ventricle. Therefore, this sound indicates that there may be an issue with the left ventricle, as it is inflexible.

Both S3 and S4 are low-frequency sounds, but doctors may hear S4 on either the left or right side of the heart. Doctors may find S4 more difficult to hear than S3, particularly in children.

Due to the inflexible ventricle, the atria must create more force to push blood down into it, and this may create a turbulent blood flow in the heart. Some diseases may make the ventricle inflexible or less compliant.

While an S3 can occur as a typical heart sound for certain individuals, an S4 always indicates that an individual has a heart condition.

If the S3 heart sound occurs in an otherwise healthy individual, doctors may not need to treat the condition. However, they have various treatment options if a person has congestive heart failure.

However, while these options cannot undo damage to the heart, they can help ease an individual’s symptoms and improve quality of life. A treatment plan may include:

  • Lifestyle changes: Include maintaining a moderate weight, eating a balanced diet, and increasing physical activity. If someone smokes, they should consider quitting.
  • Medications: These include angiotensin-converting enzyme inhibitors and beta-blockers.
  • Surgery: These techniques include a coronary artery bypass, a heart transplant, and valve replacement.
  • Devices: These devices include implantable cardioverter defibrillators and those for cardiac resynchronization therapy.

The S3 heart sound is a low-pitched sound that doctors can hear when blood rushes rapidly from the heart’s atrium into the ventricle.

Sometimes, particularly in children and athletes, it is a typical sound. However, in other cases, it may also indicate that an individual has congestive heart failure.

If someone has congestive heart failure, treatments can improve their quality of life, although they cannot undo the damage that has already occurred.