What is Tetralogy of Fallot?

By  ,  National Institute of Health
Aug 09, 2018
Quick Bites

  • Know about Tetralogy of Fallot: a congenital heart defect
  • Tetralogy of Fallot involves four heart defects
  • Vivid description of the diiference between a normal heart and a heart with the defect. 

Tetralogy (teh-TRAL-o-je) of Fallot (fah-LO) is a congenital heart defect. A congenital heart defect is a problem with the heart's structure which is present at birth. This type of heart defect changes the normal flow of blood through the heart. Tetralogy of Fallot is a rare, complex heart defect that occurs in about 5 out of every 10,000 babies. It affects boys and girls equally. Tetralogy of Fallot involves four heart defects:

  • A large ventricular septal defect (VSD).
  • Pulmonary (PULL-mon-ary) stenosis.
  • Right ventricular hypertrophy (hi-PER-tro-fe).
  • An overriding aorta.

Ventricular Septal Defect

The heart has a wall that separates the two chambers on its left side from the two chambers 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 from the left ventricle to mix with oxygen-poor blood from the right ventricle.

Pulmonary Stenosis

This defect is a narrowing of the pulmonary valve and the passage through which blood flows from the right ventricle to the pulmonary artery. Normally, oxygen-poor blood from the right ventricle flows through the pulmonary valve, into the pulmonary artery, 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 reaches the lungs.

Right Ventricular Hypertrophy

This defect occurs if 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 aorta, the main artery that carries oxygen-rich blood to the body. In a healthy heart, the aorta is attached to the left ventricle. This allows only oxygen-rich blood to flow 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 flows directly into the aorta instead of into the pulmonary artery to the lungs. 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 structure and blood flow in the interior of a normal heart. Figure B shows a heart with the four defects of tetralogy of Fallot. Babies and children who have tetralogy of Fallot have episodes of cyanosis (si-a-NO-sis). This is a bluish tint to the skin, lips, and fingernails.

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