Conotruncal Heart Defects

Defective development of the cardiac outflow tract results in congenital cardiac anomalies that are known as conotruncal heart defects (CTDs) inherited as autosomal recessive trait. Conotruncal abnormalities involve defects at the junction of the ventricular infundibulum (conus arteriosus) with the great arteries, or, embryologically, truncus arteriosus.5 The most common form of CTDs in dogs is tetralogy of Fallot, which consists of ventricular septal defect, pulmonic stenosis, overriding of the aorta, and right ventricular hypertrophy.

The location of the abnormality in the dividing wall and the heart structures involved will create different syndromes that have similar signs. For example, pulmonic stenosis causes a pot-bellied appearance due to fluid retention in the abdomen, an enlarged liver, and fluid accumulation in the hindlegs. Affected dogs may show signs of reduced ability to exercise, difficulty breathing and stunted growth. Ventricular septal defect also causes a pot-bellied appearance, with fluid retention and an enlarged liver. Affected dogs will pant a lot and will have trouble breathing. Other signs are weakness, weight loss and exercise intolerance. The gums may be bluish due to low blood oxygen levels.4

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  • Conus arteriosus - the funnel-shaped portion of the right ventricle at the entrance to the pulmonary trunk.
  • Truncus arteriosus - an artery connected with fetal heart.
  • Pulmonary trunk - a vessel arising from the conus arteriosus of the right ventricle and bifurcating into the right and left pulmonary arteries.
  • Pulmonary hypertension - a rare lung disorder characterized by increased pressure in the pulmonary artery. The pulmonary artery carries oxygen-poor blood from the lower chamber on the right side of the heart (right ventricle) to the lungs where it picks up oxygen.
  • Overriding of the aorta - a congenital anomaly occurring in tetralogy of Fallot, in which the aorta is displaced to the right so that it appears to arise from both ventricles and straddles the ventricular septal defect.
  • Right ventricular hypertrophy - enlargement of theright ventricle (chamber) of the heart. This increase in ventricular mass is often caused by pulmonary hypertension and is a contributor to fatal heart diseases.

Other canine congenital cardiac abnormalities include:

  • Cor Triatriatum
  • Coronary Vessel Anomalies
    • Arteriovenous fistula - an abnormal direct communication between an artery and a vein without passing through the capillaries.
    • Coronary artery aneurysma - a sac formed by dilation of the wall of a coronary artery.
  • Aortic Coarctation - a birth defect characterized by the narrowing of the aorta.
  • Arrhythmogenic Right Ventricular Cardiomyopathy - a congenital heart muscle defect that is characterized by infiltration of fatty and fibrous tissue into the right ventricle wall and loss of myocardial cells. (Boxer dogs)
  • Patent Ductus Arteriosus
  • Tricuspid Valve Dysplasia (Atresia)
  • Heart Septal Defects
    • Atrial septal Defect
    • Ventricular Septal Defect - developmental abnormalities in any portion of the ventricaulr septum resulting in abnormal communications between the two lower chambers of the heart.
    • Complete Atrioventricular Septal Defect - a defect consisting of ostium primum defect above, a ventricular septal defect below, and a single atrioventricular valve that is common to the right and left ventricles (formerly termed endocardial cushion defect).
Conotruncal heart defects in dogs


  1. The Keeshond defect in cardiac conotruncal development is oligogenic. Petra Werner. Human Genetics. Volume 116, Number 5/April, 2005
  2. A single major-gene defect underlying cardiac conotruncal malformations interferes with myocardial growth during embryonic development: studies in the CTD line of Keeshond dogs. Patterson DF, Pexieder T, Schnarr WR, Navratil T, Alaili R.
  3. Hereditary defects of the conotruncal septum in Keeshond dogs: Pathologic and genetic studies. Donald F. Patterson DVM, DSc, FACC , Robert L. Pyle VMD, MSc , Lodewyk Van Mierop MD, FACC , Julius Melbin VMD, PhD and Marcia Olson BA
  4. Disorder - Conotruncal heart malformation (
  5. Mario J. Garcia. Noninvasive Cardiovascular Imaging: A Multimodality Approach
  6. Ultrastructural changes in cardiac myocytes from Boxer dogs with arrhythmogenic right ventricular cardiomyopathy

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