The heart sounds are the noises, sound generated by the beating heart and the resulting movement of the blood through the heart. In cardiac auscultation, a stethoscope is used to listen for these sounds, which provide important information about the condition of the heart.

Review the sounds below to learn more.

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Normal heart sounds are associated with heart valves closing, causing changes in blood flow and can be heard as the classic lub dub sound. The lub sound is created when the ventricles contract and close the mitral and tricuspid valves. This sound is low-pitched and relatively long and represents the beginning of ventricular systole. The second heart sound, or dub, can be heard at the beginning of ventricular diastole. It is produced by closure of the aortic and pulmonary, pulmonic semilunar veins when the intraventricular pressure begins to fall.

The murmur is often described as harsh, sometimes compared to the sound of clearing one’s throat. The murmur is usually best heard at the second intercostal space to the right of the sternum. However, it is usually heard over the apex and sound is also transmitted along both sides of the neck or clavicles.

In aortic regurgitation, the backflow of blood across the aortic valve will cause a holodiastolic murmur. It is often described as a relatively high-pitched murmur, a blowing character. The murmur may be loud or soft, depending on the severity of the regurgitation. The softer the murmur, the greater the regurgitant flow. Aortic regurgitation is best heard along the lower left sternal border.

The long, low, harsh systolic murmur is typically loudest at the base of the heart and radiating to the carotids. The murmur may radiate toward the cardiac apex.

The murmur of mitral stenosis is mid-diastolic and progresses with the severity from a short decrescendo murmur to a longer crescendo murmur. In more severe cases, the murmur will stretch towards the second heart sound. In the early stage, the murmur may be only grade 1 or 2. The murmur is best heard at the apex of the heart with the patient in left lateral position. Rapid, deep inspirations or mild exercise will augment the intensity. An important sign in most patients with mitral stenosis is a loud first heart sound.

The murmur of mitral regurgitation can be of various qualities and many adjectives have been used in describing the murmur. Best heard at the apex of the heart, the murmur can vary in loudness, depending on the degree of the insufficiency and it can radiate to the left sternal edge and/or the mid-axilla and back. Words like rough, harsh, blowing are often used, but in some patients, the sound can also be of a more musical quality.

There may be a single or multiple clicks throughout systole. A single click will usually occur late in systole, while multiple clicks indicates more profound weakening and will happen in a wider array throughout systole. Many patients will have a late systolic crescendo murmur, like a quick honk. This is caused by inability of the valve to keep its closure, and it will leak towards the end of systole. The late systolic murmur may be of many various characters and can at times be extremely loud, to a point where it is easily heard without the stethoscope. MVP is best heard over the apex.

VSD will produce a systolic murmur. The classic murmur is grade ¾, holosystolic, harsh, and blowing in character. It will peak in mid-systole. It is best heard along the lower left sternal border and apex. Small and medium defects will typically produce a louder sound than a larger defect, as the blood velocity is higher. A VSD about to close will again diminish in amplitude and become faint and audible only in early systole.

The systolic murmur is harsh and blowing in nature and crescendo-decrescendo in configuration. It is best heard at the apex in the left sternal border. The crescendo-decrescendo nature of the murmur is appreciated when listening. However, due to the complexity of frequencies, the phonocardiogram will show a more rugged form.

Ejection sounds can be confused with split first heart sounds. However, ejection sounds occur somewhat later than the tricuspid component of a split S1 and is also usually louder and higher in pitch. The splitting of S1 is best heard over the fourth intercostal space, while the ejection sound is much less pronounced here. Ejection sounds are best heard over the pulmonic and aortic area and over the apex. A systolic murmur is often present with ejection sounds.

Sounds generated by rapid ventricular filling are often called gallop rhythms for the third and fourth heart sound, S3 and S4. Both sounds are of low frequency, S3 occurring in early diastole, S4 in late diastole. S3 is of low frequency and has a soft character. Fourth heart sound, S4, occurs in late diastole, just prior to the first heart sound.


Breath sounds can be classified as normal, abnormal, and adventitious, or extra sounds. Normal breath sounds are classified as tracheal, bronchial, bronchovesicular, and vesicular sounds. The patterns of normal breath sounds are created by the air moving through airways. Breath sounds are described by noting their location and their duration, how long the sound lasts; intensity, how loud the sound is; pitch, how high or low the sound is; and timing, when the sound occurs in the respiratory cycle. Abnormalities of the breath sounds can be found in duration, intensity, pitch, and timing. The term adventitious breath sounds refers to extra or additional sounds that are heard over normal breath sounds and include crackles or rales, wheezes, pleural friction rubs, and stridor.

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Normal vesicular breathing is heard over the thorax, or chest, and is lower-pitched and softer than bronchial breathing. Expiration is shorter, with no pause between inspiration and expiration. No adventitious sounds are heard.

Normal tracheal breath sounds are heard over the trachea. These sounds are harsh and sound like air being blown through a pipe.

Bronchial sounds can be heard over the large airways in the anterior chest, near the second and third intercostal spaces. The sounds have a more tubular and hollow sound than vesicular sounds, but are not as harsh as tracheal breath sounds. Bronchial sounds are loud and high-pitched with a short pause between inspiration and expiration. Expiratory sounds last longer than inspiratory sounds.

Wheezes are sounds that are heard continuously through inspiration, expiration, or both. They are caused by constriction or swelling of the airway or partial airway obstruction. Wheezes that are relatively high-pitched and have a shrill or squeaking quality are known as sibilant bronchi. They are usually heard continuously through both inspiration and expiration and have a musical quality. These wheezes occur when airways are narrowed, such as may occur during an acute asthmatic attack. Wheezes that are lower-pitched sounds with a snoring or moaning quality are known as sonorous bronchi. Secretions in large airways, for example, in cases of bronchitis may cause these sounds and they may clear somewhat with coughing.

Crackles (or rales) are caused by fluid in the small airways or atelectasis. Crackles are discontinuous sounds, intermittent, non-musical, and brief. Crackles may be heard on inspiration or expiration. Popping sounds associated with rales are created when air is forced through respiratory passages that are narrowed by fluid, mucus, or puss. Crackles often result from inflammation or infection of the small bronchi, bronchioles, and alveoli. Crackles are described as fine, medium, and coarse. Fine crackles are soft, high-pitched, and very brief. Coarse crackles are somewhat louder, lower in pitch, and last longer than fine crackles. They have been described as sounding like opening a Velcro fastener.

Pleural friction rubs are low-pitched grating or creaking sounds that result from inflamed pleural surfaces rubbing together during respiration, more often heard on inspiration than expiration. The pleural friction rub can be confused with a pericardial friction rub. To distinguish between the two, ask the patient to hold his breath briefly. If the sound stops, it’s a pleural friction rub. If the rubbing sound continues, it’s a pericardial friction rub. This is because the inflamed pericardial layers continue rubbing together with each heartbeat.

Stridor is a high-pitched, harsh sound heard during inspiration. It is caused by obstruction of the upper airway and is a sign of respiratory distress. Stridor requires immediate attention. If adventitious sounds are heard, you should assess their loudness, timing in the respiratory cycle, location on the chest wall, persistence of the pattern from breath to breath, and whether or not the sounds clear after a cough or a few deep breaths.