Issue Description An atrial septal defect is a defect or hole in
the muscular wall (the septum) that separates the right and left
atria- 2 of the 4 chambers of the heart. Other Names ASD
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.
Symptoms A small defect will be of no significance to
your dog. Dogs with no or mild clinical signs generally have a normal
lifespan. Your dog may be more susceptible to respiratory tract
With larger defects however, there will be
abnormal blood flow from the higher pressure left side of the heart
across the defect to the right side. This causes more work for the
right side of the heart , which can eventually lead to right-sided
heart failure. Signs may include respiratory difficulties, fainting,
tiring with exercise, abnormal cardiac rhythms, abdominal swelling, or
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.
Treatment Many dogs with ASDs do very well. Signs
associated with heart disease are treated when and if they develop.
Treatment includes medications to support the heart and to reduce
congestion in the lungs, a sodium-restricted diet, and exercise
Surgical closure of the defect is possible in
dogs with severe signs, but is not often considered due to the risks
and expense associated with open heart surgery.