Congenital heart defects arise from problems early in the heart's development, but there's often no clear cause. Genetics and environmental factors probably play a role. VSDs can occur alone or with other congenital heart defects.

During fetal development, a ventricular septal defect occurs when the muscular wall separating the heart into left and right sides (septum) fails to form fully between the lower chambers of the heart (ventricles).

Normally, the right side of the heart pumps blood to the lungs to get oxygen; the left side pumps the oxygen-rich blood to the rest of the body. A VSD allows oxygenated blood to mix with deoxygenated blood, causing the heart to work harder to provide enough oxygen to the body's tissues.

It's also possible to acquire a VSD later in life, usually after a heart attack.

Nov. 04, 2014