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Congenital Heart Defect (Atrial Septal Defect) in Dogs

Atrial Septal Defect in Dogs

Atrial septal defect (ASD) is a congenital heart abnormality found in both dogs and cats. It occurs when there is a hole in the interatrial septum, the wall that separates the left and right atria. This hole allows blood to flow between the atria. Normally, the blood flows into the right atrium, causing increased volume in the right side of the heart and the pulmonary vasculature. In some cases, if the pressure in the right side of the heart is too high, the blood may shunt from right to left, leading to generalized cyanosis.

Although ASD is more commonly seen in cats, accounting for 9 percent of congenital heart defects, recent data from France suggests a higher prevalence in dogs and cats combined. According to this study, ASD represents 37.7 percent of congenital cardiac defects in pooled data from both dogs and cats. Despite being less frequent in dogs, ASD remains a significant concern in veterinary cardiology.

Symptoms and Types

ASD manifests in one of three locations within the heart: the lower atrial septum (known as ostium primum defect, which is the most prevalent), near the fossa ovalis (referred to as ostium secundum defect), or craniodorsal to the fossa ovalis (known as sinus venosus defect). Common symptoms associated with ASD encompass:

  • Difficulty with exercise (exercise intolerance)
  • Episodes of fainting or loss of consciousness (syncope)
  • Respiratory difficulties (dyspnea)
  • Persistent coughing
  • Detection of a heart murmur
  • Bluish discoloration of the skin (cyanosis)
  • Accumulation of fluid in the abdomen (ascites) in the event of right-sided heart failure development.


The exact cause of atrial septal defect remains unidentified at present.


To diagnose atrial septal defect in your dog, you’ll need to provide a detailed medical history, including when the symptoms started and their nature, to the veterinarian. The vet will conduct a comprehensive physical examination and may also order a biochemistry profile, urinalysis, complete blood count, and electrolyte panel for further assessment.

For dogs with significant defects, X-rays and electrocardiograms typically reveal enlargement of the right-sided heart and lung vessels. An echocardiogram can show dilation of the right atrium and right ventricle, as well as the presence of the hole in the septum (known as a septal dropout). Additionally, arrhythmias and disturbances in intraventricular conduction may be detectable through these diagnostic tests. Doppler echocardiography is particularly useful for documenting blood flow through the hole and assessing high ejection velocity in the pulmonary artery.


Dogs experiencing congestive heart failure may require hospitalization until their condition stabilizes. Repairing the defect may involve open heart surgery, although this option can be costly. It’s important to discuss with your veterinarian the most suitable and financially feasible treatment plan for you and your pet. In certain cases of secundum-type defects, an amplatzer device could be implanted to close the hole.

Living and Management

The outlook for dogs with ASD relies on the size of the defect and any accompanying abnormalities, though it tends to range from guarded to poor. Small, isolated defects are less likely to advance, whereas primum-type defects are generally larger and carry a bleaker prognosis.

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