Heart Sound

The heart sound is caused by the turbulence of blood or vibration of structures cardiac and vascular . This turbulence is caused by the acceleration or deceleration of blood flow or the flow of blood through a hole or on a surface that is rough or uneven.


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  • 1 First heart sound
  • 2 Second heart sound
  • 3 Third heart sound
  • 4 Fourth heart sound
  • 5 Bibliography

First heart sound

The first heart sound (S1) is caused by the sudden deceleration of the blood against the closed mitral and tricuspid valves . The mitral valve closes somewhat earlier than the tricuspid valve, but the proximity of its closure and the much greater intensity of the noise caused by the mitral valve closing makes the first noise sound unique. When the S1 sounds “split”, a disorder should be suspected.

The most useful aspect of S1 auscultation is its intensity. S1 should always be louder at the apex than the second heart sound (S2) and should be approximately equal to S2 at the bottom. Causes of severe S1 include increased adrenergic tone, thyrotoxicosis, anemia, exercise, or anxiety. An increased intensity of S1 can also be a sign of mitral stenosis , but it is an unreliable sign, since mitral stenosis can also present with normal or reduced intensity S1.

Decreased S1 intensity is a sign of elevated end-diastolic pressure. It can appear in case of prolongation of the PR interval, congestive heart failure, coronary heart disease and aortic insufficiency . A variable S1 is heard when the end-diastolic pressure of the ventricle varies from cycle to cycle. This situation occurs in second and third degree heart block and in other heart rhythms with atrioventricular (AV) dissociation.

Second heart sound

S2 is caused by the sudden deceleration of a large column of blood in the aorta and in the pulmonary artery against closed semilunar valves. A normal S2 is unfolded, with the aortic component (A2) appearing before the pulmonary component (P2). During expiration, the S2 sounds unique, although it is sometimes audibly split during expiration in healthy young people. There is an inspirational split of A2 and P2, with A2 being auscultated first. S2 splitting abnormalities, including wide splitting, (paradoxical) reversal of splitting, lack of splitting and fixed splitting.

Third heart sound

The third heart sound (S3) is heard in the early phase of diastole, immediately after opening of the tricuspid and mitral valves when ventricular filling is faster. The S3 is a low intensity sound, usually smooth. It is best heard with the patient placed in the left lateral decubitus position and with the stethoscope bell resting gently on the cardiac apex.

S3 is caused by passive relaxation of the ventricle associated with rapid initial diastolic filling. When the ventricular walls reach their point of maximum distension, there is a deceleration of the blood flow and a low intensity vibration of the ventricles, which cause S3. An S3 is considered normal, a “physiological S3,” in patients under the age of 30 who do not have any other signs of heart disease. An S3 that is heard in patients aged between 30 and 40 years is indicative. In this age group, symptoms such as thyrotoxicosis, pregnancy, anxiety, and post-exercise states can cause S3 not associated with heart disease. An S3 that is heard after age 40 should be considered a probable sign of heart disease.

An S3 that is heard after age 40 can be caused by three types of heart disease: diastolic ventricular overload, ventricular dysfunction, and constrictive pericarditis. Diastolic ventricular overload is most often caused by mitral regurgitation, although persistent ductus arteriosus (DAP), ventricular septal defect (IVC), and aortic regurgitation can also cause ventricular overload S3. S3 heard in these states of diastolic ventricular overload is almost invariably associated with a murmur. Clinically, S3 associated with ventricular dysfunction is the most important that the family doctor must recognize. An S3 not associated with a state of diastolic ventricular overload, such as mitral regurgitation, suggests global ventricular dysfunction.

Ventricular dysfunction is associated with a change in ventricular compliance. An S3 auscultated in the context of ventricular dysfunction suggests dilated cardiomyopathy, long-standing or transient ischemic heart disease, or decompensated hypertension. The S3 of ventricular dysfunction should be considered a finding with serious prognostic implications. Pericardial disease, including constrictive pericarditis , the pericardial effusion , the metastatic tumor , infection or disease connective tissue, can cause S3. In the case of pericardial disease, what creates S3 is the sudden deceleration of ventricular relaxation and filling caused by pericardial pathology.

Fourth heart sound

The fourth heart sound (S4) is known as the “atrial gallop.” It is caused by abrupt distension and vibration of the ventricles at the time of atrial contraction. The S4 is best heard with the patient placed in the left lateral decubitus position and with the stethoscope bell placed without pressing on the cardiac apex. S4 is a sign of loss of ventricular compliance. An S4 is rarely detected in the absence of heart disease.

There is controversy over whether an S4 can be considered normal in the geriatric population, where there is a certain “physiological loss” of ventricular compliance; however, as a general rule, an audible S4 should be considered pathological. As the underlying heart disease progresses, the ventricle loses compliance and diastolic ventricular pressure increases. At this point, the effect of atrial contraction on ventricular filling decreases.

In contrast to S3, which intensifies as ventricular compliance decreases, S4 weakens as underlying ventricular dysfunction progresses. The underlying cardiac pathology that leads to the appearance of an S4 is similar to the factors that cause an S3, with two important additions; While an S3 is not auscultated in hypertrophic cardiomyopathy or in left ventricular hypertrophy (LVH) caused by hypertension , auscultation of an S4 is frequent in these pictures.

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