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S3 Heart SoundEdit

An S3 heart sound is an additional heart sound that can accompany normal rhythm or indicate underlying cardiac issues. It occurs in early diastole, after the closing of the aortic and pulmonic valves (S2), and is often described as a soft, low-frequency “ventricular gallop.” In healthy children and young adults, S3 can be a physiological finding, but in older adults it may reflect volume overload or reduced ventricular compliance and can be a sign of heart disease. The sound is typically best heard at the apex of the heart with the patient in the left lateral decubitus position, using the bell of a stethoscope during end-exhalation. See S1 heart sound and S2 heart sound for context on the other normal sounds, and ventricular gallop for the common descriptive term.

S3 results from rapid filling of a compliant ventricle during early diastole, followed by sudden tensing of the ventricular wall and adjacent structures. This mechanism makes S3 a low-frequency sound that is often difficult to detect in individuals with thicker chests, higher heart rates, or poor acoustic windows. The traditional listening site is the left-lateral position, though S3 can sometimes be heard at other locations depending on body habitus and pathology. Its presence must be interpreted together with the overall clinical picture, including signs of heart failure, volume status, and coronary or valvular disease. See diastole and left ventricle for background on the cardiac phase and chamber involved, and stethoscope for the instrument used to listen.

Physiology and mechanics

  • Origin: S3 arises during rapid ventricular filling in early diastole, when the inflowing blood interacts with a relatively compliant ventricle.
  • Timing: It appears after S2, in early diastole, and is best heard with the patient in a position that brings the apex closer to the chest wall.
  • Dependency on heart rate and rhythm: A faster heart rate or tachycardia can make S3 harder to hear or can shift its timing relative to the cardiac cycle.
  • Influencing factors: Body position, chest wall thickness, and lung volume affect detectability; a gentle bell and patient cooperation improve sensitivity.
  • Relation to other sounds: S4, by contrast, occurs in late diastole just before S1 and reflects a stiff ventricle; distinguishing S3 from S4 is a key skill in auscultation. See S4 heart sound for comparison.

Clinical significance

  • Physiologic S3: In children, adolescents, and many young adults, S3 can be a normal variant tied to a highly compliant ventricle and robust circulatory status. It is sometimes called a “physiologic gallop.”
  • Pathologic S3: In adults, especially those over about 40 years old, the appearance of S3 often signals volume overload and potential left-sided heart disease, such as dilated cardiomyopathy or congestive heart failure. It can accompany conditions like mitral regurgitation or other states that increase venous return and ventricular filling pressures.
  • Prognostic context: When S3 accompanies signs of heart failure or reduced ejection fraction, it may correlate with worse prognosis and guide management decisions. In some patients with preserved ejection fraction, S3 may be present without overt symptoms, raising questions about timing and scope of further testing. Clinicians typically corroborate auscultation with imaging, most commonly echocardiography and assessment of ventricular function.
  • Population considerations: In athletes or individuals with high cardiac output, S3 may appear without pathology, whereas in others it prompts evaluation for underlying disease. The interpretation hinges on the complete clinical scenario, including risk factors, symptoms, and other physical examination findings.

Diagnosis and evaluation

  • Auscultation technique: With the patient relaxed and in approximate end-exhalation, place the bell of the stethoscope at the apex in the left lateral decubitus position and listen for low-frequency sounds.
  • Complementary testing: If an S3 is detected or suspected to be clinically meaningful, clinicians may order or perform echocardiography to assess ventricular size, wall thickness, and function; additional tests may include ECG, chest imaging, and laboratory markers of heart failure.
  • Differential considerations: Distinguishing S3 from other diastolic sounds (such as S4 or noise from rapid heart rate) is important, as treatment implications diverge depending on the underlying cause. See S4 heart sound for comparison.

History and terminology

  • Terminology: An S3 sound is often described as a “ventricular gallop.” The term S3 has historical roots in describing the third heart sound in the canonical sequence of S1, S2, S3, and S4. See gallop for broader context and related phrases.
  • Evolution of practice: Recognition of physiologic S3 in young people and the more ominous connotation of S3 in older adults reflect advances in imaging and a nuanced understanding of diastolic function. This evolution informs how clinicians approach patients who present with an S3 on exam.

See also