Equis ISSN 2398-2977

Heart: ventricular septal defect

Synonym(s): VSD

Contributor(s): Karen Blissitt, Christopher Brown, Wendy Furness, Lesley Young


  • The most common congenital cardiac defect.
  • Cause: congenital.
  • Signs: variable.
  • Diagnosis: auscultation of characteristic murmur/murmurs and visualization of lesion on echocardiography.
  • Treatment: none currently available; palliative if heart failure results.
  • Prognosis: dependent on position and size.
Print off the Owner factsheet on Heart murmurs to give to your clients.



  • A defect in the ventricular septum of varying size.
  • Usually the defect is in the membranous portion of the ventricular septum beneath the tricuspid and aortic valve.
  • Defects in the membranous portion are caused by lack of fusion of the atrioventricular endocardial cushion and the muscular ventricular septum.
  • Occasionally the defect occurs in the infundibular or outflow portion of the membranous septum with the result that shunted blood enters the RV close to the pulmonary valve (subpulmonic).
  • Defects in the muscular portion (rare) are caused by abnormal development of the bulbous cordis (most common in Arabians).
  • May occur alone or as part of a complex of malformations, eg Tetralogy of Fallot   Heart: tetralogy of Fallot  .


  • Hemodynamic effect of a VSD depends on the size and amount of blood shunted through it.
  • Blood flows from the high pressure left ventricle to the low pressure right ventricle.
  • If a large proportion of the LV stroke volume is shunted this will   →    pulmonary overcirculation and volume overload primarily of the LA
  • Increased pulmonary and left atrial pressures can result in secondary right ventricular failure   Heart: tricuspid regurgitation  .
  • Flow across the defect depends both on the size of the defect and on the pressure differential between the LV and RV; an increase in RV pressure will   →    a decreased flow across the VSD.
  • A reverse shunt (Eisenmenger's syndrome) can theoretically occur if there is substantial increase in RV pressure, although this has not yet been reported in the horse, possible because the equine pulmonary circulation is not as reactive to increased flow as that of other species, eg the dog or human.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Patteson M (2010) Prepurchase examination in horses: detection and significance of heart murmurs. In Pract 32 (9), 438-443 VetMedResource.
  • Morgan R (2010).Ventricular septal defect in a four-year-old Thoroughbred - what are the consequences for horse and owner? UK Vet 15 (6), 4-6 VetMedResource.
  • Crochik S S, Barton M H, Eggleston R B & Kent M (2009) Cervical vertebral anomaly and ventricular septal defect in an Arabian foal. Equine Vet J 21 (4), 207-211 VetMedResource.
  • Froehlich W, Wlaschitz S, Reidelberger K & Reef V B (2006) Tricuspid valve endocarditis in a horse with ventricular septal defect. Equine Vet Educ 18 (4), 172-176 VetMedResource.
  • Reppas G P et al (1996) Multiple congenital cardiac anomalies and idiopathic thoracic aortitis in a horse. Vet Rec 138 (1), 14-16 PubMed.
  • Reef V B et al (1995) Evaluation of ventricular septal defects in horses using two-dimensional and Doppler echocardiography. Equine Vet J Suppl 19, 86-95 PubMed.
  • Wilson R B et al (1987) Right atrioventricular atresia and ventricular septal defect in a foal. Cornell Vet 77 (2), 187-191 PubMed.
  • Pipers F S et al (1985) Echocardiographic detection of ventricular septal defects in large animals. JAVMA 187 (8), 810-816 PubMed.
  • Reef V B et al (1985) Cardiovascular disease in the equine neonate. Vet Clin North Am Equine Pract (1), 117-129 PubMed.
  • McClure J J et al (1983) Complete transposition of the great arteries with ventricular septal defect and pulmonary stenosis in a Thoroughbred foal. Equine Vet J 15 (4), 377-380 PubMed.
  • Lombard C W et al (1983) Ventricular septal defects in the horse. JAVMA 183 (5), 562-565 PubMed.
  • Bonagura J D et al (1983) Multiple congenital cardiac anomalies and idiopathic thoracic aortitis in a horse. JAVMA 182 (4), 396-402 PubMed.
  • Vitums A et al (1982) Pulmonary atresia with dextroposition of the aorta and ventricular septal defect in three Arabian foals. Vet Pathol 19 (2), 160-168 PubMed.
  • van der Luer R J et al (1978) A rare congenital cardiac anomaly in a foal. Vet Pathol 15 (6), 776-778 PubMed.
  • Glazier D B et al (1975) Ventricular septal defect in a 7-year old gelding. JAVMA 167 (1), 49-50 PubMed.