Introduction

• 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 flow viscosity changes, eg with anemia and hypovolemia.
  • 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 Cardiovascular system: examination. 
• Normal heart sounds: Cow heart sounds
• Murmurs may classified in three ways:
  • Innocent murmurs are frequently heard in young animals and may disappear by maturity.
  • Physiological/functional murmurs may be heard in association with anemia, tachycardia, pyrexia.
  • Pathological murmurs may be caused by congenital cardiac diseases:
    • Patent ductus arteriosus Patent ductus arteriosus. 
    • Pulmonic stenosis.
    • Aortic stenosis.
    • Septal defect Ventricular septal defect. 
    • Atrioventricular regurgitation.
    • Or acquired cardiac disease:
      • Degenerative valvular disease (very rare in cattle).
      • Endocarditis Endocarditis. 
      • Cardiomyopathy resulting in changes in chamber size Cardiomyopathy. 

Characterization of murmurs

Normal heart sounds

Abnormal heart sounds

Further Reading

Publications

Refereed Papers

• Recent references from PubMed and VetMedResource.