Blood flows through the heart and generates noises known as heart sounds. These noises occur due to heart valves opening and closing as the heart pumps blood. A doctor can gain valuable information by listening to heart sounds, which may help them reach a diagnosis of a heart condition.

The human heart is a muscular chest organ located slightly left of the center. It rhythmically beats roughly 100,000 times per day to pump blood throughout the body.

Blood flows through the heart in one direction, similar to a one-way traffic system. Heart valves help control the direction of blood flow, acting like doors opening and closing with every heartbeat. Doctors refer to the noise from the opening and closing of valves as heart sounds.

This article looks at heart sounds, how to measure them, and what abnormal heart sounds and murmurs may indicate.

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Heart sounds refer to the noises that occur when blood flows through the heart chambers as valves open and close during the cardiac cycle. The heart has four chambers:

  • the right atrium
  • the right ventricle
  • the left atrium
  • the left ventricle

Valves at the bottom of each atrium empty into the two ventricles.

There are two phases in the cardiac cycle: systole and diastole. The former is when the ventricles contract and pump blood out, and the latter is when the ventricles relax and fill with blood. These two phases make up the heartbeat.

The cardiac cycle features four sounds. It is much easier to hear the first two noises, “lub” and “dub,” which are high pitched. The third and fourth sounds are low pitched and often quieter. Sometimes, if the doctor can hear the third and fourth sounds, it may indicate a potential problem with heart function.

First sound

Vibrations from closing the two valves known as the mitral and tricuspid valves cause the first “lub” heart sound. These valves close to prevent blood from flowing into either atrium after the two ventricles contract to pump blood into the pulmonary artery and aorta.

As the valves close, this creates an audible vibration as the first heart sound. As the valves close almost simultaneously, it usually creates a single sound. Clinically, this noise corresponds to the pulse, and doctors refer to it as S1. A split S1 occurs when the time difference between the two valves increases. Split heart sounds may indicate a problem.

Second sound

The second sound occurs when the ventricles relax to receive blood from the atria after pumping blood, which is the diastole phase of the cardiac cycle. The valves close, which causes vibrations, and results in the second “dub” sound.

If the aortic valve closes before the pulmonic valve, it may cause two distinct sounds, which experts may refer to as aortic and pulmonic components. The pulmonic valve may close after the aortic, as the right ventricle can fill with more blood, leading to a slightly longer ejection time.

Doctors may also refer to the second heart sound as an S2, and if there is a time difference in the closure, it is a split 2.

Third sound

The third sound is low pitched. When blood rushes into the relaxing ventricle after the opening of the atrioventricular valve, the rush of blood may be audible.

Although the sound is standard in some people, including children and young adults, in others, it can signal disease, such as congestive heart failure. The third heart sound may be abnormally audible as a ventricular or protodiastolic gallop, which describes a galloping sound.

Fourth sound

The fourth heart sound is also low pitched and very quiet. When present, this sound typically occurs due to the atrium contracting against a stiff ventricle.

Some doctors may refer to the fourth sound as an atrial gallop. This sound often suggests the presence of cardiac disease, typically involving a decrease in ventricular compliance and resistance to filling. This may include conditions such as:

A doctor will listen to the heart using a stethoscope, called auscultating. A stethoscope has a chest piece with two attachments called a bell and a diaphragm, which connect via a tube to two earpieces.

A doctor can use the diaphragm attachment to hear higher pitched noises, such as the first and second heart sounds. They can then use the bell attachment to listen for low pitched sounds, such as the third and fourth heart sounds. In some cases, an amplified stethoscope may be necessary to hear the third and fourth sounds.

A doctor may listen to different areas of the heart, including:

  • the base, between the bottom left of the heart and the sternum
  • the apex, which is at the bottom left of the heart
  • the aortic and pulmonary areas to the left and right of the sternum

Aside from the four heart sounds, a doctor may hear abnormal sounds or murmurs, which could indicate heart problems.

A heart murmur is not one of the four heart sounds. A murmur may sound like a rasping or whooshing noise due to a turbulent flow of blood through the heart valves.

A heart murmur may be harmless, known as an innocent heart murmur. This type of murmur does not usually cause symptoms, and doctors do not consider them serious.

Other heart murmurs could indicate a problem in the heart. These murmurs can result from problems with heart valves, such as aortic stenosis and aortic regurgitation.

Medical professionals grade murmurs on a scale according to their loudness. They will also categorize the murmur as systolic or diastolic, depending on the stage of the heartbeat. Some heart murmurs may be continuous, meaning a doctor can hear them during both the systole and diastole.

The doctor may also perform tests to check a person’s heart function with a murmur. These may include:

Clicks and high pitched sounds

A doctor may also hear abnormal clicking, snapping, or high-pitched noises, which are not one of the four heart sounds. These may not indicate any problem and could be natural. However, they could also indicate a valve malfunction and may require further investigation to check heart health.

Blood flows through the heart during a cardiac cycle and generates four heart sounds. A doctor may hear these sounds using a stethoscope. Heart sounds can provide valuable information about the health of a person’s heart and may help with a diagnosis.

The first and second heart sounds are high pitched and constitute the heartbeat’s healthy “lub” and “dub” sounds. The third and fourth heart sounds are low pitched and may indicate problems with the functioning of the heart. A doctor may hear other noises through a stethoscope, such as heart murmurs or clicks. While some noises may be harmless, others may indicate cardiac problems.