Tetralogy of Fallot is a congenital cardiac malformation in which the heart has four anatomical defects, which change the normal flow of blood through the heart. In tetralogy of Fallot the left ventricle pumps poor-oxygen blood to the rest of the body which results in cyanotic conditions in babies; this is a bluish tint to the skin, lips, and fingernails. This low oxygenation of blood is due to the mixing of oxygenated and deoxygenated blood in the left ventricle due to a ventricular septal defect (a hole), and preferential flow of the mixed blood from both ventricles through the aorta because of the obstruction to flow through the pulmonary valve. This is known as a right-to-left shunt.
A heart with tetralogy of Fallot may present: 1) a narrowing of the right ventricular outflow tract due to pulmonary valve stenosis; 2) a ventricular septal defect, which is an abnormal hole that abnormally communicates the two heart ventricles; 3) an aortic valve with biventricular connection, that is, it is situated above the ventricular septal defect and connected to both the right and the left ventricle; 4) a right ventricle hypertrophy (with a thickened muscular wall).
Although tetralogy of Fallot is usually diagnosed during infancy, sometimes it may not be detected until later in life, depending on the severity of the defects and symptoms. With early diagnosis followed by appropriate treatment, most children with tetralogy of Fallot live relatively normal lives, though they'll need regular medical care and may have restrictions on exercise.