Tetrology of Fallot is a congenital heart defect. A combination of four abnormalities in the heart allow oxygen-rich and oxygen-depleted blood to mix. The resulting low-oxygen blood then circulates through the body.

What is going on in the body?

Normally, the right side of the heart pumps oxygen-poor blood to the lungs. Once enriched by oxygen, this blood returns to the left side of the heart to be pumped to tissues throughout the body. A wall called the septum separates the two sides of the heart.

Tetrology of Fallot is a combination of four heart defects that are apparent at birth. These defects allow the blood supplies to mix so that the blood sent to cells throughout the body is low in oxygen. Blood flow to the lungs is decreased, too. Not getting enough oxygen can cause vital organs to fail.

What are the causes and risks of the condition?

The cause of tetrology of Fallot is unknown. However, a baby is more likely to be born with tetrology of Fallot if the mother has one of the following conditions: