Heart sounds

Front of thorax, showing surface relations of bones, lungs (purple), pleura (blue), and heart (red outline). The locations of best auscultation for each heart valve are labeled with "M", "T", "A", and "P".

First heart sound: caused by atrioventricular valves – Mitral (M) and Tricuspid (T).

Second heart sound caused by semilunar valves – Aortic (A) and Pulmonary/Pulmonic (P).

Heart sounds are the audible acoustic phenomena created by the mechanical functioning of the heart. These sounds, primarily caused by the closing of heart valves and the resultant rush of blood, are an important part of clinical cardiology, providing critical information about cardiac health and functionality. Using a stethoscope, a medical professional can evaluate these sounds for any irregularities or abnormalities.

Basic Heart Sounds

In a healthy adult, the cardiac cycle, or heartbeat, typically produces two distinctive heart sounds: the first heart sound (S₁) and the second heart sound (S₂). These sounds are often colloquially referred to as a lub (S1) and a dub (S2), respectively.

S1, the first heart sound, is caused by the closure of the atrioventricular valves (the mitral valve and tricuspid valve) at the beginning of ventricular systole. S2, the second heart sound, is produced by the closure of the semilunar valves (the aortic valve and pulmonary valve) at the end of ventricular systole.

Additional Heart Sounds

Beyond the fundamental lub-dub, additional heart sounds may be identified during cardiac auscultation. These can include heart murmurs, adventitious sounds, and gallop rhythms (specifically, the S₃ and S₄).

Heart murmurs are sounds produced by turbulent blood flow within the heart or its vessels. This turbulent flow requires a pressure difference of at least 30 mmHg between the heart chambers, with the blood flowing from the higher-pressure chamber to the lower-pressure chamber. Depending on which chamber is pressure-dominant, this can lead to a Left-to-right shunt or a Right-to-left shunt.

Murmurs can be physiological (benign) or pathological (indicative of a disease). Pathological murmurs often result from stenosis (narrowing of a heart valve opening) or regurgitation (incompetent valve closure, leading to backflow of blood). The timing of different murmurs in the cardiac cycle can aid in diagnosing the underlying cause.

Primary Heart Sounds

Diagram showing relations of opened heart to front of thoracic wall. Ant. Anterior segment of tricuspid valve. A O. Aorta. A.P. Anterior papillary muscle. In. Innominate artery. L.C.C. Left common carotid artery. L.S. Left subclavian artery. L.V. Left ventricle. P.A. Pulmonary artery. R.A. Right atrium. R.V. Right ventricle. V.S. Ventricular septum.

First Heart Sound (S1)

The first heart sound (S1) represents the beginning of the cardiac cycle and is produced by the closure of the atrioventricular valves. These include the mitral valve on the left side of the heart and the tricuspid valve on the right. The closure of these valves prevents blood from flowing back into the atria when the ventricles contract during systole. This sound is typically described as a "lub" and is best heard with the diaphragm of a stethoscope at the lower left sternal border and the apex of the heart.

Second Heart Sound (S2)

The second heart sound (S2) signals the end of systole and the start of diastole. It is produced by the closure of the semilunar valves—the aortic valve and pulmonary valve—which prevents blood from flowing back into the ventricles when they relax. The sound of S2 is often described as a "dub" and is best heard at the upper left sternal border and the second left intercostal space.

Pathological Heart Sounds

Murmurs

Heart murmurs are the sounds of turbulent blood flow within the heart or the great vessels. They often reflect disorders of the heart valves, but can also be caused by increased blood flow through a normal valve (for instance, in cases of fever, anemia, or pregnancy), defects in the walls of the heart, or abnormal connections between the heart and major blood vessels. Murmurs can occur during systole, diastole, or both.

Third Heart Sound (S3)

The third heart sound (S3) is an additional sound produced by the rapid filling and expansion of the ventricles during the early part of diastole. It is often a normal finding in children and young adults but can signify heart failure or volume overload in older adults. An S3 is typically low pitched and is best heard with the bell of a stethoscope at the apex of the heart.

Fourth Heart Sound (S4)

The fourth heart sound (S4) is produced by the atria contracting forcefully in an effort to overcome a stiff or hypertrophic ventricle. This sound is not normally heard in healthy individuals and is usually a sign of a pathological condition such as hypertensive heart disease or ischemic heart disease. An S4 is typically low pitched and best heard with the bell of a stethoscope at the apex of the heart.

See also

• Pulse
• Precordial examination
• Benign pediatric heart murmur
• Iambic pentameter, a metre in poetry which follows a similar rhythm to the human heartbeat
• Pulsatile tinnitus – hearing a heartbeat sound in one or both ears
• Souffle (heart sound)

External links

• Heart Sounds – Heart Murmurs. practicalclinicalskills.com

Heart sounds Resources
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