Types of Abnormal Heart Sounds

By Rosalie McDonough, MD, MSc - Posted in Clinical Education
Abnormal heart sounds play a crucial role in diagnosing various cardiovascular conditions. Recognizing and understanding these sounds is essential to accurate clinical assessment and management. In this article, we explore the types of abnormal heart sounds, their associated pathologies, as well as practical auscultation tips.
Types of Abnormal Heart Sounds

Overview 

In general, abnormal heart sounds encompass any auditory findings beyond S1 and S2. These include “extra” heart sounds, e.g. S3 and S4, and murmurs. Each abnormal heart sound is associated with specific cardiovascular conditions and thus has unique diagnostic implications.  

“Extra” heart sounds

Although under the category of abnormal heart sounds, S3 and S4 are not always pathological, particularly in younger patients or when heard during certain phases of the cardiac cycle. However, they may be indicators of underlying cardiac conditions and should thus not be overlooked or disregarded. 

S3
S3 is an abnormal heart sound that occurs during the early phase of diastole, shortly (~0.15 s) after the second heart sound (S2). It's often described as a low-frequency, “thumping” sound heard during cardiac auscultation. While it is sometimes present in healthy individuals, it is more commonly associated with conditions that lead to volume overload of the ventricles, such as heart failure or mitral regurgitation. It can also be present in non-cardiac causes, such as hyperthyroidism. 
 
Tips to enhance auscultation of S3:
  • Have patient lie on their left side.
  • Use the bell of the stethoscope (good for low frequency sounds).
  • Apply firm pressure.
  • Listen at different locations.
  • Have the patient exhale and hold their breath.
      S4
      S4 is another abnormal heart sound that typically occurs in the late phase of diastole, just before the first heart sound (S1). S4 is a soft, low-frequency sound that can be heard during cardiac auscultation. While it may occasionally be heard in healthy individuals, it is more often a sign of decreased ventricular compliance, indicating conditions such as hypertrophic cardiomyopathy, systemic hypertension, or aortic stenosis. Its presence can also signify advanced age or myocardial infarction.
       
      Tips to enhance auscultation of S4:
      • Have patient lie on their left side.
      • Use the bell of the stethoscope (good for low frequency sounds).
      • Apply firm pressure.
      • Listen at different locations.
      • Focus on rhythm and timing of heart sounds during diastole to detect subtle S4.  
      S3 / S4 overview
       
      Heart sound Timing Character Point of maximum intensity Physiological Pathological Enhanced by
      S3 Early diastole Low frequency At cardiac apex and 4th intercostal space on the right


      Rapid ventricular filling in diastole in children and adolescents       		Diastolic volume overload in conditions like mitral regurgitation, heart failure, or hyperthyroidism Patient lying on left side, bell of stethoscope, expiration, after mild exertion
      S4 Late diastole Soft, low frequency At cardiac apex and 4th intercostal space on the left Atrial contraction against elevated left ventricular pressure (e.g., stiffening) Patient lying on left side, bell of stethoscope
       

       

      Murmurs

      Heart murmurs are abnormal sounds heard during cardiac auscultation and are typically indicative of underlying structural or functional abnormalities within the heart. While some murmurs may be benign, others can signify significant cardiac pathology, requiring further evaluation and management. Understanding the characteristics of heart murmurs, including their timing, intensity, and radiation, is essential for accurate diagnosis and appropriate patient care. 

      Type Location Characteristics Auscultation Tips
      Systolic Murmurs
      Aortic Stenosis RUSB - Crescendo-descendo
      - Radiation to the carotids
      - May have an ejection click with the point of maximum intensity over the cardiac apex      		 Loudness of the murmur does not correlate with the severity of the stenosis
      Mitral Regurgitation Apex - Holosystolic, "band"-shaped
      - Radiation to the left axilla
      - Possible 3rd heart sound, faint 1st heart sound      		 -
      Pulmonary Stenosis LUSB - "Harsh" or crescendo-descendo
      - Separated from the 1st heart sound
      - Pulmonary "ejection click" in mild to moderate forms
      - Potential splitting of the 2nd heart sound      		 -
      Tricuspid Regurgitation LLSB - Holosystolic murmur Accentuated by inspiration
      Ventricular Septal Defect LLSB - Harsh, holosystolic murmur
      - Fixed, breath-independent, split 2nd heart sound      		 -
      Diastolic Murmurs
      Aortic Regurgitation LLSB - Early diastolic
      - Decrescendo
      - "Austin-Flint" murmur      		 Have patient lean forward, exhale, and hold
      Mitral Stenosis Apex - Mid-diastolic
      - "Rumbling"      		 Have patient lie on their left side
      Pulmonary Hypertension LUSB - "Louder" S2, with possible splitting
      - Variant: Graham-Steell murmur      		 -
      Continuous Murmurs
      Patent ductus arteriosus (PDA), arteriovenous (AV) fistulas LUSB - Persistent abnormal communication between blood vessels
      -Present throughout the entire cardiac cycle
      - Machinery" or "to-and-fro" quality, where there's a persistent abnormal connection between the distal aortic arch and pulmonary trunk       		-
       
       

      How to:

      Auscultation points:
      • Aortic valve: RUSB, 2nd intercostal space right, parasternal
      • Pulmonary valve: LUSB, 2nd intercostal space left, parasternal
      • Tricuspid valve: LLSB, 4th intercostal space right, parasternal
      • Mitral valve: Apex, 5th intercostal space left, midclavicular line
      What to listen/look for:
      • Heart rhythm and rate
      • Is there a pulse deficit?
      • Are abnormal heart sounds audible?
        • Where are they most clearly heard? Point of maximal intensity (PMI)
        • When are they heard? Systolic vs. diastolic vs.continuous
        • Sound character (high-frequency, low-frequency)
        • Temporal pattern (PCG)
        • Radiation?
       
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      About the Author

      Rosalie McDonough, MD, MSc
      Rosalie McDonough, MD, MSc - Clinician Scientist

      Rosalie McDonough, MD, MSc, is a clinician scientist with a diverse background in medical research and clinical practice. She earned her Master of Science degree from McGill University in Montreal, Canada, later completing her medical degree at the University Medical Center Hamburg-Eppendorf in Hamburg, Germany. Dr. McDonough’s career has spanned various fields within medicine, focusing on clinical research and health technology. Her interests have encompassed cardiopulmonary disease, lung cancer, molecular cardiology, occupational medicine, and acute ischemic stroke imaging. She is currently the Senior Manager of Medical Affairs at Eko Health.