What Is Tetralogy of Fallot?

Tetralogy of Fallot is a congenital (kon-JEN-i-tal) heart defect (a problem with the heart's structure that's present at birth). Congenital heart defects change the normal flow of blood through the heart. This rare and complex heart defect occurs in about 5 out every 10,000 babies. It affects boys and girls equally.

Tetralogy of Fallot involves four defects:

• A large ventricular (ven-TRICK-u-lar) septal defect (VSD)
• Pulmonary (PULL-mon-ary) stenosis (steh-NO-sis)
• Right ventricular hypertrophy (hy-PER-trow-fee)
• An overriding aorta

Ventricular Septal Defect

The heart has a wall that separates the chambers on its left side from those on its right side. This wall is called a septum. The septum prevents blood from mixing between the two sides of the heart.

A VSD is a hole in the part of the septum that separates the ventricles—the lower chambers of the heart. The hole allows oxygen‑rich blood to flow from the left ventricle into the right ventricle instead of flowing into the aorta, the main artery leading out to the body.

Pulmonary Stenosis

This is a narrowing of the pulmonary valve and the passageway through which blood flows from the right ventricle to the pulmonary arteries. Normally, oxygen-poor blood from the right ventricle flows through the pulmonary valve into the pulmonary arteries and out to the lungs to pick up oxygen. In pulmonary stenosis, the heart has to work harder than normal to pump blood, and not enough blood can get to the lungs.

Right Ventricular Hypertrophy

This is when the right ventricle thickens because the heart has to pump harder than it should to move blood through the narrowed pulmonary valve.

Overriding Aorta

This is a defect in the location of the aorta. In a healthy heart, the aorta is attached to the left ventricle, allowing only oxygen-rich blood to go to the body. In tetralogy of Fallot, the aorta is between the left and right ventricles, directly over the VSD. As a result, oxygen‑poor blood from the right ventricle can flow directly into the aorta instead of into the pulmonary artery to the lungs.

Overview

Together, these four defects mean that not enough blood is able to reach the lungs to get oxygen, and oxygen-poor blood flows out to the body.

Normal Heart and Heart With Tetralogy of Fallot

Figure A shows the normal structure and blood flow in the interior of the heart. Figure B shows a heart with the four defects of tetralogy of Fallot.

Babies and children with tetralogy of Fallot have episodes of cyanosis (si-a-NO-sis), which is a bluish tint to the skin, lips, and fingernails. Cyanosis occurs because the oxygen level in the blood is below normal.

Tetralogy of Fallot must be repaired with open‑heart surgery, either soon after birth or later in infancy. The timing of the surgery depends on how severely the pulmonary valve is narrowed.

Outlook

Over the past few decades, the diagnosis and treatment of tetralogy of Fallot has greatly improved. As a result, the majority of children with this heart defect grow to adulthood. However, they need lifelong medical care from a specialist to make sure they stay as healthy as possible.