Diagnosis

Often, as with most heart defects, the first indication of a problem is when your veterinarian hears a heart murmur on your pup's first physical examination. There may be exercise intolerance or respiratory difficulties. This usually occurs in an older dog or a young pup with a large defect where congestive heart failure has already developed.

Some low-grade murmurs are "innocent" and disappear by 6 months of age, but if the murmur is significant, your veterinarian will suggest a diagnostic workup to determine the cause. He or she will listen very carefully to your dog's heart to determine the point of maximal intensity of the murmur and when the murmur occurs during the cardiac cycle. Other diagnostic aids include chest x-rays and an electrocardiogram (ECG), which typically show enlargement of the right side of the heart. Further tests such as an ultrasound can be performed to determine the size of the defect.

Causes

The mode of inheritance is not known for ASDs, but many cardiac defects are believed to have a polygenic mode of inheritance, with variable expression. However recent studies suggest a series of single major gene defects may be responsible for inherited heart defects in dogs.