Causes of Heart Murmurs

Heart murmurs are produced by turbulent flow across an abnormal valve, septal defect or outflow obstruction. ‘Innocent’ murmurs caused by increased volume or velocity of flow through a normal valve occur when stroke volume is increased, e.g. during pregnancy, in athletes with resting bradycardia or children with fever.



Causes of systolic murmurs

  • Increased flow through normal valves
  • ‘Innocent systolic murmur’: fever, athletes (bradycardia → large
  • stroke volume), pregnancy (cardiac output maximum at 15 weeks)
  • Atrial septal defect (pulmonary flow murmur)
  • Severe anaemia
  • Normal or reduced flow though a stenotic valve
  • Aortic stenosis
  • Pulmonary stenosis
  • Other causes of flow murmurs
  • Hypertrophic cardiomyopathy (obstruction at subvalvular level)
  • Aortic regurgitation (aortic flow murmur)

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