The third heart sound or S₃ is a rare extra

heart sound Heart sounds are the noises generated by the beating heart and the resultant flow of blood through it. Specifically, the sounds reflect the turbulence created when the heart valves snap shut. In cardiac auscultation, an examiner may use a stet ...

that occurs soon after the normal two "lub-dub" heart sounds (S₁ and S₂). S₃ is associated with

heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, ...

Physiology

It occurs at the beginning of the middle third of

diastole Diastole ( ) is the relaxed phase of the cardiac cycle when the chambers of the heart are re-filling with blood. The contrasting phase is systole when the heart chambers are contracting. Atrial diastole is the relaxing of the atria, and ventricu ...

, approximately 0.12 to 0.18 seconds after S₂. This produces a rhythm classically compared to the cadence of the word "

Kentucky Kentucky ( , ), officially the Commonwealth of Kentucky, is a state in the Southeastern region of the United States and one of the states of the Upper South. It borders Illinois, Indiana, and Ohio to the north; West Virginia and Virginia ...

" with the final syllable ("''-CKY''") representing S₃. One may also use the phrase "Slosh’-ing-IN" to help with the cadence (Slosh S₁, -ing S₂, -in S₃), as well as the pathology of the S₃ sound, or any other number of local variants. S₃ may be normal in people under 40 years of age and some trained athletes but should disappear before middle age. Re-emergence of this sound late in life is abnormal and may indicate serious problems like

. The sound of S₃ is lower in pitch than the normal sounds, usually faint, and best heard with the

bell A bell is a directly struck idiophone percussion instrument. Most bells have the shape of a hollow cup that when struck vibrates in a single strong strike tone, with its sides forming an efficient resonator. The strike may be made by an inte ...

of the

stethoscope The stethoscope is a medical device for auscultation, or listening to internal sounds of an animal or human body. It typically has a small disc-shaped resonator that is placed against the skin, and one or two tubes connected to two earpieces. ...

. It has also been termed a ventricular gallop or a protodiastolic gallop because of its place in early diastole. It is a type of

gallop rhythm A gallop rhythm refers to a (usually abnormal) rhythm of the heart on auscultation. It includes three or four sounds, thus resembling the sounds of a gallop. The normal heart rhythm contains two audible heart sounds called S1 and S2 that give th ...

by virtue of having an extra sound; the other gallop rhythm is called S₄. The two are quite different, but they may sometimes occur together forming a quadruple gallop. If the

heart rate Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excr ...

is also very fast (

tachycardia Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal ( ...

), it can become difficult to distinguish between S₃ and S₄ thus producing a single sound called a summation gallop. S₃ is a dull, low-pitched sound best heard with the bell placed over the cardiac apex with the patient lying in the left lateral decubitus position. This heart sound when present in a child or young adult implies the presence of a supple ventricle that can undergo rapid filling. Conversely, when heard in a middle-aged or older adult, an S₃ is often a sign of disease, indicating increased ventricular filling due to congestive

or severe mitral or tricuspid regurgitation.

Causes

S₃ is thought to be caused by the oscillation of blood back and forth between the walls of the ventricles initiated by the inflow of blood from the atria. The reason the third heart sound does not occur until the middle third of diastole is probably that, during the early part of diastole, the ventricles are not filled sufficiently to create enough tension for reverberation. It may also be a result of tensing of the

chordae tendineae The chordae tendineae (tendinous cords), colloquially known as the heart strings, are inelastic cords of fibrous connective tissue that connect the papillary muscles to the tricuspid valve and the mitral valve in the heart. Structure The chor ...

during rapid filling and expansion of the ventricle.

Associations

It is associated with

, caused by conditions which have:

Rapid ventricular filling

Mitral regurgitation Mitral regurgitation (MR), also known as mitral insufficiency or mitral incompetence, is a form of valvular heart disease in which the mitral valve is insufficient and does not close properly when the heart pumps out blood. Section: Valvular H ...

- this is when one of the mitral valve leaflets that usually stop blood flowing from the left ventricle to the left atrium fails, allowing blood into the atria during

systole Systole ( ) is the part of the cardiac cycle during which some chambers of the heart contract after refilling with blood. The term originates, via New Latin, from Ancient Greek (''sustolē''), from (''sustéllein'' 'to contract'; from ...

. This means that the left atrium will be overfilled, leading to rapid ventricular filling when the mitral valve opens.Lilly, Leonard et al. Pathophysiology of Heart Disease, Fourth Edition, page 37. * Elevated left atrial and left ventricular filling pressures, usually a result of a stiffened and dilated left ventricle *

Ventricular septal defect A ventricular septal defect (VSD) is a defect in the ventricular septum, the wall dividing the left and right ventricles of the heart. The extent of the opening may vary from pin size to complete absence of the ventricular septum, creating one ...

- this is a hole in the wall between the two ventricles, which allows rapid filling from the other ventricle.

Poor left ventricular function

* Post-MI - the death of tissue in the ventricular wall due to loss of blood supply causes wall areas which do not move as well as normal (

hypokinesia Hypokinesia is one of the classifications of movement disorders, and refers to decreased bodily movement. Hypokinesia is characterized by a partial or complete loss of muscle movement due to a disruption in the basal ganglia. Hypokinesia is a sy ...

), or not at all (akinesia), meaning they relax more slowly, so the ventricular filling is relatively too rapid. *

Dilated cardiomyopathy Dilated cardiomyopathy (DCM) is a condition in which the heart becomes enlarged and cannot pump blood effectively. Symptoms vary from none to feeling tired, leg swelling, and shortness of breath. It may also result in chest pain or fainting. Co ...

- the ventricular walls are abnormal for a variety of reasons, and become thin and stiff so do not relax well. S3 can also be due to tricuspid regurgitation, and could indicate hypertensive heart disease. In conditions affecting the

pericardium The pericardium, also called pericardial sac, is a double-walled sac containing the heart and the roots of the great vessels. It has two layers, an outer layer made of strong connective tissue (fibrous pericardium), and an inner layer made ...

or diseases that primarily affect the heart muscle ( restrictive cardiomyopathies) a similar sound can be heard, but is usually more high-pitched and is called a 'pericardial knock'.The S3 can also be confused with a widely split S2, or a mitral opening snap, but these sounds are typically of much higher pitch and occur closer to the onset of S2.

Treatment

The condition itself does not need to be treated, but rather the underlying cause requires correction. Depending on the

etiology Etiology (pronounced ; alternatively: aetiology or ætiology) is the study of causation or origination. The word is derived from the Greek (''aitiología'') "giving a reason for" (, ''aitía'', "cause"); and ('' -logía''). More completely, ...

the gallop rhythm may resolve spontaneously.

References

External links

* {{Cardiovascular system symptoms and signs Cardiology