An atrioventricular septal defect (AVSD) is a heart defect that occurs when a hole or holes are present in the heart wall, and the valves that control blood flow between the chambers are incorrectly formed. Atrioventricular septal defects (AVSD), also known as atrioventricular canal defects or endocardial cushion defects, cause blood flow from the heart to the rest of the body not to be properly controlled. Atrioventricular septal defects (AVSD) can lead to the blood having less oxygen or too much blood flowing into the lungs. Atrioventricular septal defects (AVSD) are most common in infants with Down syndrome. Approximately 15 to 20 percent of newborns with Down Syndrome will have an atrioventricular septal defect (AVSD).
Causes of atrioventricular septal defects (AVSD) are still relatively unknown, but may include genetic and environmental factors. Babies born with Down syndrome may also have chromosomal trigger.