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Tetralogy of Fallot is the most common cyanotic congenital heart defect. The overall incidence is about 5 in 10,000 individuals. Originally described in 1672, it was named after Dr. Étienne-Louis Arthur Fallot in 1888. Tetralogy of Fallot consists of 4 findings, a ventricular septal defect (hole in the lower wall of the heart), pulmonary stenosis (narrowing in the outflow of blood to the lungs), overriding aorta, and right ventricular hypertrophy. The first two findings, the VSD and pulmonary stenosis, are what determine the significance of tetralogy of Fallot.

The aorta and the pulmonary artery are the two main arteries ("Great Arteries") that carry blood away from the heart.  In the normal heart, the pulmonary artery is connected to the right ventricle and carries oxygen-poor blue blood returning from the body to the lungs, where it becomes oxygenated.  The oxygen-rich red blood returning from the lungs passes into the left side of the heart where it is pumped by the left ventricle out the aorta. In the normal heart, circulation to the lungs (pulmonary) and the circulation to the body (systemic) are in series, forming one continuous circuit that crosses in the heart, like two rings fusing to form a figure 8.

The arterial switch operation is the preferred method of repairing transposition of the great arteries in this day and age. In transposition of the great arteries, the aorta arises from the right ventricle and the pulmonary artery from the left ventricle. Deoxygenated, or blue blood, returning from the body is sent directly back out to the body again. Likewise, oxygenated, or red blood returning from the lungs is sent right back out to the lungs. Mixing is only possible if there is an atrial communication and/or a patent ductus arteriosus. In the absence of successful mixing, transposition of the great arteries is usually fatal.

Tricuspid atresia is a type of congenital heart disease in which the tricuspid valve fails to develop properly.  Typically there is simply a plate of tissue where the normal tricuspid valve should be. This results in no direct communication between the right atrium and right ventricle.  This defect was first described in 1817.  Today, studies have estimated its incidence at around 5-6 per 100,000 live births.  As many as 20% of those affected also have other heart defects.