Congenital Heart Defect (Atrial Septal Defect) in Dogs

Atrial Septal Defect in Dogs

Atrial septal defect (ASD) is a congenital heart anomaly that enables blood flow between the left and right atria via the interatrial septum (the separating wall). Typically, the blood will shunt into the right atrium, causing a volume overload to the right atrium, right ventricle, and pulmonary vasculature, which can sometimes lead to pulmonary hypertension. However, if right-sided pressures are too high, shunting may occur right to left, causing generalized cyanosis.

ASD is more common in cats (9 percent of congenital heart defects) than dogs (0.7 percent), though a recent study from France suggests a higher incidence, with ASD accounting for 37.7 percent of congenital cardiac defects in pooled data from dogs and cats.

Symptoms and Types

ASD occurs in one of three locations: lower atrial septum (ostium primum defect, which is the most common), near the fossa ovalis (ostium secundum defect), or craniodorsal to the fossa ovalis (sinus venous defect). Common signs associated with ASD include:

  • Exercise intolerance
  • Fainting/loss of consciousness (syncope)
  • Trouble breathing (dyspnea)
  • Coughing
  • Heart murmur
  • Bluish skin (cyanosis)
  • Fluid buildup in the abdomen (ascites) if right-sided heart failure develops


The underlying cause of atrial septal defect is currently unknown.


You will need to give a thorough history of your dog’s health, including the onset and nature of the symptoms, to the veterinarian. He or she will then perform a complete physical examination as well as a biochemistry profile, urinalysis, complete blood count, and electrolyte panel.

X-rays and electrocardiograms will typically show right-sided heart and lung vessel enlargement in patients with large defects, while an echocardiogram may reveal right atrial and right ventricular dilation and the actual hole (a septal dropout). Arrhythmias and intraventricular conduction disturbances may also be visible using these diagnostic procedures. To document the blood flow through the hole and high ejection velocity through the pulmonary artery, doppler echocardiography is useful.


A wall or partition that is designed to divide and separate


Pertaining to the lungs


A cavity within a bone; may also indicate a flow or channel


An in-depth examination of the properties of urine; used to determine the presence or absence of illness


a) A cavity in certain animals b) Term refers to a rear chamber in the heart or a cavity in the brain


The prediction of a disease’s outcome in advance


Fainting; the respiratory and circulatory systems are suspended for a time


High blood pressure


The superior chamber in an animal’s heart.


The collection of fluid in the peritoneal cavity.


The widening of something


Having a hard time breathing; breathing takes great pains


A procedure that is used to evaluate the health and structures of the heart


A large blood vessel that transports blood out of the heart.

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