The left and right side of the heart are separated by a wall called the septum. Some people are born with a hole in either the upper septum (atrial septal defect) or the lower septum (ventricular septal defect). When these defects are present, oxygen-rich blood from the lungs may mix with oxygen-poor blood returning from the body.

Common symptoms of a ventricular defect may include shortness of breath, hard or fast breathing and frequent respiratory infections. Common symptoms of an atrial defect may include difficulty breathing, shortness of breath with activity, heart palpitations (rapid, noticeable heart beats) and frequent respiratory infections.