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 physical examination. Sometimes there is exercise intolerance or respiratory difficulty, but this is usually 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. S/he will listen very carefully to your dog's heart to determine where the murmur is loudest and when it occurs during the cardiac cycle. Other diagnostic aids include chest x-rays and an electrocardiogram (ECG). Echocardiography (an ultrasound) is generally required to determine the location and severity of a ventricular septal defect.

Causes

Before birth, the heart starts out as a single tube which gradually differentiates into 4 chambers during embryological development. Abnormalities can arise at several steps in the process, resulting in defects in the muscular walls that normally separate the heart into the right and left atria, and the right and left ventricles. The result is abnormal blood flow in the heart with varying effects in the dog, depending on the size and location of the defect.