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Defect of the Ventricular Septum in Cats


Ventricular Septal Defect in Cats


A ventricular septal defect (VSD) is an irregular communication in the ventricular septum, the wall that separates the ventricles (the two lower chambers of the heart) from one another. A VSD typically results in blood being diverted, or shunted, from one side of the heart to the other. The direction and volume of the shunt are determined by the size of the defect, the relationship of the pulmonary and systemic blood vessel resistances, and the presence of other anomalies.


Most VSDs in small animals are subaortic (below the aortic valve) and have a right ventricular hole that is beneath the septal leaflet of the tricuspid valve. In addition, most VSDs in cats are small and therefore restrictive (i.e., the difference between left and right ventricular pressures is maintained). Moderate-sized VSDs are only partially restrictive and result in various degrees of high blood pressure in the right ventricle. Large VSDs, meanwhile, have an area that is as large as or larger than the open aortic valve in the left ventricle. They are nonrestrictive, and right ventricular pressure is the same as the body’s blood pressure. Only moderate and large defects impose a pressure load upon the right ventricle.


This is the most common congenital cardiac malformations in cats.


Symptoms and Types


Cats generally present no symptoms of the defect (asymptomatic); however symptoms commonly associated with ventricular septal defects include:


  • Difficulty breathing
  • Exercise intolerance
  • Fainting
  • Cough
  • Pale gums (only if pulmonary hypertension causes a right to left shunt)
  • Increased rate of heart beat



The underlying cause for ventricular septic defects are unknown, though a genetic basis is suspected.




You will need to give your veterinarian a thorough history of your cat's health and onset of symptoms. Your veterinarian will perform a thorough physical exam on your cat, with a complete blood profile, chemical blood profile, complete blood count, urinalysis and an electrolyte panel to rule out other concurrent diseases.


Imaging techniques like thoracic X-rays may help to detect larger VSDs, which would cause a left (or even a generalized) enlarged heart from the increased flow of blood through the heart. High blood pressure in the lungs, chronic heart failure and right to left shunts may be visualized as well. 


A two-dimensional echocardiographic study, which uses sonographic imaging to view the activity of the heart, may demonstrate heart enlargement. The right heart will also be enlarged if the defect is moderate-sized or large, or if there are other heart abnormalities in addition to VSD.



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