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)
