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Heart SoundsEdit

Heart sounds are acoustic events produced by the mechanical and hemodynamic events of the cardiac cycle. They are most reliably detected with a stethoscope and are a foundational element of the clinical examination in Cardiology and broader medical practice. In a normal exam, two principal sounds—S1 and S2—mark the start and end of systole, while additional sounds such as S3 and S4, together with various murmurs and rubbing sounds, can signal a range of cardiac conditions. The interpretation of heart sounds relies on timing within the cardiac cycle, the quality and intensity of the sounds, and the patient’s physiology, including heart rate and respiration. See also cardiac auscultation and Stethoscope for practical listening techniques.

Physiology and production of heart sounds

  • S1, the first heart sound, is primarily produced by the closure of the mitral and tricuspid valves at the onset of systole. It is typically loudest at the apex and can vary with heart rate, respiration, and valve anatomy. For more on valve anatomy, see Mitral valve and Tricuspid valve.
  • S2, the second heart sound, results from the closure of the aortic and pulmonic valves at the end of systole. It is commonly described as the “DUB” and consists of two components: A2 (aortic) and P2 (pulmonic). The interval between A2 and P2 can widen with inspiration due to increased right-sided flow; see Aortic valve and Pulmonic valve for details.
  • S3, sometimes called a ventricular gallop, is an extra sound that may appear in early diastole during rapid LV filling. In young, healthy individuals it can be normal, but in adults it often reflects volume overload or systolic dysfunction. See S3 heart sound for more.
  • S4, the atrial gallop, occurs late in diastole just before S1 and is associated with a stiff ventricle, commonly due to long-standing hypertension, LV hypertrophy, or infiltrative disease. See S4 heart sound for more.
  • Other audible phenomena include murmurs (turbulent flow across a valve or lesion) and pericardial rubs (inflammation of the pericardium). These are discussed in the sections on murmurs and pericardial disease and linked terms such as Murmur and Pericardial friction rub.

Normal heart sounds

  • The classic sequence—S1 followed by S2—reflects the start and end of systole. S1 is best heard at the apex in the left lateral decubitus position, while S2 is often best heard at the base of the heart. The relative loudness of S1 and S2 can vary with age, cardiac rhythm, and body habitus.
  • Splitting of S2 is a normal variant in many individuals, most evident with deep inspiration. During expiration, the gap between A2 and P2 narrows as venous return changes. Persistent and abnormal splitting can indicate specific pathologies such as right bundle branch block or pulmonary hypertension.
  • The stethoscope and technique, including the use of the diaphragm for higher frequencies and the bell for lower frequencies, influence the sensitivity to these sounds. See Stethoscope and Auscultation for more.

Additional sounds and murmurs

  • S3 and S4 are not always present. When they are, their clinical significance depends on age, comorbidity, and hemodynamics. S3 in older adults can indicate heart failure or volume overload; in younger people it can be physiologic.
  • Murmurs are sounds produced by turbulent flow, often from valvular disease (stenosis or regurgitation) or septal defects. They are classified by timing (systolic vs diastolic), quality, location, and radiation, and graded by intensity on the Levine scale. For a fuller discussion of murmurs, see Murmur.
  • Pericardial friction rubs are scratchy sounds heard with inspiration in cases of pericarditis or pericardial inflammation; see Pericarditis for context.
  • The clinical relevance of each sound depends on the overall picture, including history, exams, and, when indicated, imaging and laboratory studies. See Cardiac imaging for how auscultatory findings complement echocardiography and other modalities.

Auscultation technique and clinical practice

  • Preparation and stance: patient position (upright, supine, or left lateral decubitus) changes the acoustic window and can enhance certain sounds. The left lateral decubitus position improves mitral area listening, while upright listening can accentuate aortic murmurs. See Cardiac auscultation for a structured approach.
  • Stethoscope choices: the diaphragm helps detect high-frequency components (S1, S2, most murmurs), while the bell is more sensitive to low-frequency sounds (some murmurs and S3/S4 in particular situations). See Stethoscope for device details.
  • Listening sites: the four classic auscultation areas are the aortic (right 2nd intercostal space), pulmonic (left 2nd intercostal space), tricuspid (left lower sternal border), and mitral (apex, left 5th intercostal space at the midclavicular line). Proper labeling and interpretation often involve correlating findings across these areas. See Aortic valve, Pulmonic valve, Tricuspid valve, and Mitral valve for anatomical context.
  • Integration with diagnosis: heart sounds are most informative when integrated with patient history and other data. Contemporary practice often uses imaging—especially echocardiography—to confirm suspected valvular disease or structural pathology identified by auscultation. See Echocardiography for details.

Historical and educational context

  • The art and science of listening to the heart has long underpinned cardiovascular assessment. Pioneers such as René Laennec revolutionized examination techniques with the invention of the stethoscope, shaping modern Cardiology and bedside medicine. See René Laennec for historical context.

See also