Tetralogy of Fallot
Print Friendly, PDF & Email

almostadoctor app banner for android and iOS almostadoctor iPhone, iPad and android apps almostadoctor iOS app almostadoctor android app


Tetralogy of FallotR-to-L shunt – CYANOTIC
THE most common cause of cyanotic heart disease – but only accounts for <10% of all congenital cardiac abnormalities
Has four features:
  • Large VSD – usually so large that pressures in the left and right sides of the heart are equal
  • Right ventricular outflow obstruction – often pulmonary valve stenosis – due to the overriding aorta, and sometimes, muscle overgrowth around the valve.
  • Overriding of the aorta – this is where the aorta is position directly over the ASD – and not over the left ventricle. The aorta will receive blood from both the left and right ventricles, reducing the concentration of oxygenated blood that goes into system circulation.
  • Right ventricular hypertrophy – resulting from the other three factors
Tetralogy of Fallot
Tetralogy of Fallot. This file is taken from wikimedia commons and is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.


  • The most common cyanotic heart condition
  • The most common cause of blue baby syndrome

Clinical features

  • Cyanosis – possibly at rest depending on severity
  • Dyspnoea on feeding / crying / exertion
  • Failure to thrive
  • Murmur – usually harsh, and at the left sterna edge, grade 3-6. Due to pulmonary outflow obstruction rather than VSD
    • Systolic thrill may also be present

‘Tet Spells’

  • Sudden onset dyspnoea / cyanosis
  • Typically triggered by an event that slightly reduces O2 concentration, e.g. crying, defecating, feeding, distress
  • Can be a vicious cycle, as the tet spell can make the child more distressed
  • Sometimes preceded by rapid, deep breathing
  • This increases venous return to the right ventricle, whose output is mainly via the aorta – and thus this is part of the vicious cycle
  • Tet spells typically occur in those aged 2-4M
  • Severe spells can lead to death
  • Some toddlers may adopt a squatting position – which reduces venous return to the heart, and may help increase blood O2


  • Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
  • Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.
  • Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy

Read more about our sources

Related Articles

Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

This Post Has One Comment

  1. Bobby

    great article… a little correction…
    Overriding of the aorta – you have written ‘ the aorta is positioned directly over the ASD’ … it read VSD.

Leave a Reply