A septal defect is essentially a hole in the heart that creates an opening between two chambers. Many dogs and cats with small septal defects can benefit from surgery, which if successful, is essentially curative. Many of these surgeries require referral to a large veterinary center (Eldredge, et. al., 2007). Large septal defects have a poor prognosis, and affected dogs and cats are at risk of congestive heart failure and sudden death.
As stated above, the best method of treatment for a small septal defect is to obtain surgery from a large veterinary center. Your vet will know more about what is available in your area. For more information on some leading vet centers, see Heart Disease: Resources: Veterinary Cardiology Resources.