Heart Diseases in Birds

If heart problem were not congenital, there are several dietary possibilities.

Cardiomyopathy has been associated with thyroid diseases, anemia, malnutrition, metabolic disorders, parasitic infections, pancreatitis, toxemias and neoplasia. That is quite a list! So if the diet has insufficient levels of iodine (thyroid consequences), poor iron and protein content (anemia), poor available nutrients for absorption and any combination of deficiencies or excesses, then cardiac and many other problems are more likely to become clinically apparent. 
Therefore, it is prudent as a breeder to use diets that have a clinical record as being healthful and productive. Avian nutrition has learned much of this from poultry researchers, and today's diets, if fed appropriately, make nutritional cardiomyopathies very unlikely. In birds, the right atrioventricular valve thickens with an increase in workload.
This increase in demand predisposes the bird to right atrioventricular valvular insufficiency that results in a murmur. Perhaps it took your bird a while to develop these changes before the murmur could be heard. Parasitic infections can be responsible for anemias, and, again, these conditions must be severe enough to result in clinical signs. Anemias produce murmurs in rare cases, but it is due to a decreased viscosity in the blood flow that blows away the normal hemodynamic flow pattern. Again this produces a murmur just like a weak or sloppy valve. Pancreatitis can be due to many things. The most common one in pet bird practice is heavy metal toxicity. This is probably going to be diagnosed with more and more frequency in aviaries. I have seen this problem in aviaries and it will be found if veterinarians and breeders run the appropriate tests.

Infectious disease can cause myriad heart and general systemic problems. Bird hearts (chickens) have been researched extensively for the effects of viral, bacterial and fungal infections. Many cardiovascular malformations can be easily experimentally induced. Intraventricular septal defects are common in avian hearts and result in right sides heart failure, which then results in AV valve disease (murmurs).

I will list here some common cause of heart lesion in birds:

PERICARDITIS (Inflammation of the sack around the heart)
Listeria (bacteria)
E. coli septicemia
Chlamydia
Salmonella
Reovirus
Concurrent respiratory disease 

CARDIOMEGALY (heart enlargement)
Polyomavirus (better vaccinate)
Hemochromatosis (iron storage disease)
Salmonella
Pasteurella
 
MYOCARDITIS (Inflammation of the heart muscle itself)
Listeria
E. coli septicemia
Pastuerella
Chlamydia
Polyomavirus
Avian serositis virus
Sarcocystis
Proventricular dilatation disease
Selenium and vitamin E deficiencies 

HYDROPERICARDIUM (Fluid accumulation in the sack around the heart)
Polyomavirus
Reovirus
Furazolidone toxicity
Genectics 

As you can see, the list is long. The diagnostics would include an electrocardiogram, blood cultures, pericardial fluid culture, ultrasound, complete blood count, cardiac imaging via angiography and endoscopy to examine the pericardium and epicardium, if possible. It is commendable to the veterinary profession that the examining veterinarian performed a physical examination and recommended return of the bird. It is commendable that the store refunded the money, and it will be commendable and good for your reputation and continued success when you replace the bird.

Anytime I recommend a breeder to a client, I tell the client that I cannot guarantee they will not buy a sick bird but that I can guarantee the breeders I recommend will stand by their baby. If the bird is sick, the breeder will replace it or refund their money. As long as the breeder I am referring to continues these practices, they get our referrals. Today, with the Internet, I refer to people literally all over the world, and nothing substitutes for a reputation of honesty.