The first heart sound, or S1, is the “lub” of a normal heartbeat.
Normalheart soundsS1 and S2are created by one or more heart valves closing.
The valves close to create a tight seal, preventing blood from flowing backward through the heart.
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S1 reflects the closing of the tricuspid and mitral valves.
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What Makes the Noise?
The S1 noise is made when thetricuspidandmitralvalves close as blood cycles through theheart’s four chambers.
When the tricuspid and mitral valves close, the ventricles squeeze (contract) and pump blood.
A single cardiac cycle consists of two componentssystoleanddiastole.
When Does S1 Occur?
S1 occurs at the beginning of systole.
What Does a Loud S1 Sound Mean?
Mitral stenosis andtachycardiaare two health conditions associated with a loud S1.
The S1 is loud in mitral stenosis because the mitral valve leaflets are thick and close abruptly.
Types of tachycardia include:
What About a Soft or Muffled Sound?
Mitral regurgitation and severe congestive heart failure are two conditions associated with a soft and muffled S1.
Another classic finding of mitral regurgitation is aholosystolicmurmur, best heard at the apex of the stethoscope’s diaphragm.
Treatment for S1 Sound Deviations
The treatment of S1 sound deviations depends on the underlying cause.
LikeS1,S2is a high-pitched sound best heard with the stethoscope’s diaphragm.
Murmurs may be “innocent,” occurring harmlessly in young children or during pregnancy.
Many heart conditions are lifelong and require close observation and minor adjustments to treatment plans over time.
S1 happens when two of the heart’s valves, the mitral and tricuspid valves, close.
Merck Manual Professional Version.
American Heart Association.Tachycardia: fast heart rate.
2022;15(9):e007960.
doi:10.1016/j.hrthm.2019.03.002
Armstrong GP.Mitral regurgitation.
Merck Manual Professional Version.
American Heart Association.Heart failure signs and symptoms.
2024;11:1372543. doi:10.3389/fcvm.2024.1372543
National Heart, Lung, and Blood Institute.Heart treatments.
Meyer TE.Patient education: mitral regurgitation (Beyond the Basics).
In: UpToDate, Gottlieb SS (Ed), Wolters Kluwer
Meyer TE.Auscultation of heart sounds.
In: UpToDate, Gersch BJ, (Ed), Wolters Kluwer
Gupta JI, Shea MJ.Cardiac auscultation.
Merck Manual Professional Version.
