Atrial Septal Defects (ASD)

Patty Khuly


Should the heart fail to form properly in an animal embryo, a break in the wall separating two of the chambers of the heart may remain open. In the case of atrial septal defects (ASDs), the resulting “hole in the heart” occurs between the right and left atriums, both of which are instrumental in pumping blood into the lungs and the rest of the body, respectively.

In atrial septal defects, the blood tends to get “shunted” from the right side to the left as a result of the relatively high pressures built up in the blood that returns from the rest of the body after the oxygen has been depleted from it. That means that blood often does not get properly pushed into the lungs, leading to inadequate oxygen in the blood and an excess of non-oxygenated blood backing up in the rest of the body.

Thankfully, most pets affected by this condition are not severely affected, which allows some to enjoy normal lifespans and many others to live almost-normal lives free of most symptoms. Others are not so fortunate and may suffer severe forms, but currently, these are considered in the minority for this rare condition that primarily affects dogs.

The current thinking is that dogs most severely challenged by ASD are those with other heart defects that likely developed in tandem with the defect itself.

Symptoms and Identification

Dogs with symptoms of ASD are often identified by the significant heart murmur their veterinarian detects on physical examination. Others may offer no such obvious signs and will display evidence of possible heart problems either through exercise intolerance (sluggishness or tiring easily during exercise) and/or cyanosis (noted by a blue tinge to the tongue or mucous membranes). Those most insignificantly affected by ASD will have their problems picked up incidentally on routine X-rays.

After these dogs have been flagged as possible sufferers of the problem, diagnosis is best achieved through simple chest X-rays (which almost always demonstrate an enlargement in the right side of the heart) and echocardiography (ultrasound of the heart) with doppler (demonstrating the flow of blood) to elucidate the abnormal change in the dimensions of the heart and the blood flow through it.

Affected Breeds

Any breed of cat or dog may be affected but, in dogs, it is most prevalent among:


Treatment for ASD varies according to the size of the defects and the presence of other heart abnormalities. No treatment until symptoms are noted is the typical approach for this condition, though medical management through heart drugs may be necessary in moderately to severely affected dogs.

Severely affected dogs (usually those with multiple heart problems) have been treated surgically, but most of these patients have done very poorly, leading veterinarians to believe that even the most terribly affected are best left managed through drugs.

Veterinary Cost

Unfortunately, most animals with ASD require expensive echocardiograms (heart ultrasounds) on a fairly regular basis (which can cost up to $500-$600 in some hospitals). Luckily, however, the cost of cardiac drugs, if necessary, are usually not insurmountable.


Preventing ASD is a hereditary concern. Therefore, preventing reproduction in any affected pet is considered critical. First degree relatives (littermates and parents) must be screened prior to breeding while screening dogs and cats from highly affected breeds prior to breeding is strongly recommended.


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