Canis ISSN: 2398-2942

Murmur: overview

Contributor(s): Serena Brownlie, Peter Darke, Mark Rishniw


  • Cardiac murmurs are audible sounds that:
    • Occur during the cardiac cycle and result from turbulence in laminar blood flow or vibration of certain cardiac structures (chordae).
  • Blood flow turbulence may develop for a number of different reasons:
    • When blood flow velocity increases.
    • When blood passes through a narrowed vessel, or a narrow orifice, with a high velocity.
    • When a jet of regurgitant blood strikes a chamber or vessel wall.
  • While intrathoracic blood flow turbulence generates the majority of audible vibrations detected on clinical examination, it is also possible for peripheral vascular abnormalities, eg arteriovenous fistulas, to produce blood flow turbulence and similar audible vibrations (called 'bruits' or 'hums').
  • Cardiac murmurs are distinct from the normal heart sounds caused by passive valve closure and should also be distinguished from systolic clicks, gallop rhythms, and normal and abnormal respiratory sounds.
  • Murmurs may be:
    • Innocent.
    • Physiological/functional.
    • Pathological.
  • Innocent murmurs are frequently heard in young animals and may disappear by maturity. They may be more common in mature dogs than previously reported, especially in certain breeds.
  • Physiological/functional murmurs may be heard in association with anemia, tachycardia, pyrexia.
  • Pathological murmurs may be caused by congenital cardiac disease Congenital heart disease: overview :
    • Patent ductus arteriosus.
    • Pulmonic stenosis.
    • Aortic stenosis.
    • Septal defect.
    • Atrioventricular regurgitation.
  • Or acquired cardiac disease:
    • Degenerative valvular disease.
    • Endocarditis.
    • Dilated cardiomyopathy.
Print off the owner factsheet on Heart murmurs in dogs Heart murmurs in dogs to give to your client.Follow the diagnostic tree for Heart murmurs in dogs Heart murmurs in dogs.

Characterization of murmurs

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Abnormal heart sounds

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Further Reading


Refereed papers