Although a physician can often find an ASD by listening for a heart murmur (abnormal heart sound), the majority of ASD patients have no symptoms. Therefore, the defect may be found when a person is 3 or 4 years old, or when a person is 30 or 40 years old.

If symptoms do appear in childhood, they may include frequent chest colds and upper respiratory infections that may require hospitalization. If the defect is large enough, side effects may include malnutrition (despite a normal diet) coupled with stunted growth. This is because the heart is doing extra work, thus demanding more calories and slowing the metabolism. Finally, the more congested the lungs become, the more susceptible a person is to pulmonary hypertension, a condition in which blood pressure in the lung's blood vessels is high. Symptoms of pulmonary hypertension include:

The symptoms of ASD are similar to other less serious medical conditions or problems. If individuals, especially children, exhibit these symptoms, they should be evaluated by a physician.