Ventricular septal defects (VSD) classified according to location

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  Membranous: Defect in outflow tract of left ventricle, immediately below aortic valve

  
  
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  Muscular: Defect in muscular portion of septum, anywhere from cardiac apex to base

  
  
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  Outlet: Defect in outflow tract of right ventricle, below pulmonary valve

  
  
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  Inlet: Located posterior and inferior to membranous septum, beneath septal leaflet of tricuspid valve

Small muscular ventricular septal defects may not be visible on grayscale or color Doppler

Atrioventricular septal defect

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  Large VASD as well as VSD

  
  
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  Missing crux (middle) of heart

  
  
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  Single atrioventricular valve

Signal dropout at membranous-muscular junction of septum potential pitfall

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  Try to image perpendicular to ventricular septum

Look for echogenic dot at edge of defect

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  Normally no echo at site of transition from muscular to membranous septum

Confirm on long-axis view if seen on apical 4-chamber view and vice versa

Look for septal continuity with aortic annulus in left ventricular outflow tract view to exclude membranous VSD

Use color Doppler to confirm blood flow across defect

Obtain dedicated fetal echo

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  Associated cardiac abnormalities present in 50%