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 that’s present at birth. This type of heart defect changes the normal flow of blood through the center. Tetralogy of Fallot is a rare, complex heart defect that happens in about 5 out of every 10,000 infants. It affects boys and girls equally. Tetralogy of Fallot involves four core defects:
Right ventricular hypertrophy (hi-PER-tro-fe).
An overriding aorta.

Ventricular Septal Defect
The heart has a wall which separates the two chambers on the left side by the two chambers onto its right side. This wall is called a septum. The septum prevents blood from mixing between the 2 sides of the heart. A VSD is a hole at the part of the septum that divides the ventricles, the lower chambers of the heart. The hole allows oxygen-rich blood in the left ventricle to mix with oxygen-poor blood in the right ventricle.

Pulmonary Stenosis
This defect is a narrowing of the pulmonary valve and the passage by which blood flows from the right ventricle into the pulmonary artery. Usually, oxygen-poor blood from the right ventricle flows through the pulmonary valve, into the pulmonary artery out to the lungs to pick up oxygen. In pulmonary stenosis, the heart needs to work harder than normal to pump blood vessels, and not enough blood reaches the lungs.

Right Ventricular Hypertrophy
This flaw occurs if the right ventricle thickens since the heart must pump harder than it must move blood through the narrowed pulmonary valve.

Overriding Aorta
This is a defect in the aorta, the major artery that carries oxygen-rich blood to the body. In a healthy heart, the aorta is attached to the left ventricle. This permits only oxygen-rich blood to flow into your system. In tetralogy of Fallot, the aorta is between the right and left ventricles, right over the VSD. Because of this, oxygen-poor blood in the ideal ventricle flows directly into the aorta instead of into the pulmonary artery into the lungs. Collectively, these four defects mean that insufficient blood can reach the lungs to get oxygen, and oxygen-poor blood flows from the body.

Regular Heart and Heart With Tetralogy of Fallot
Figure A displays the structure and blood flow in the interior of a normal heart. Figure B shows a hub with the four flaws of tetralogy of Fallot. Babies and children that 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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