Tetralogy of Fallot: Tetralogy of Fallot is combination of four defects of the heart which occur by birth (congenital heart disease). There is a large defect in the wall between the left and right ventricles (ventricular septal defect), aorta overriding the defect, thickening of the wall of the right ventricle (right ventricular hypertrophy) and narrowing of outflow of the right ventricle (pulmonary stenosis). This results in reduced blood supply to the lungs and mixing of deoxygenated and oxygenated blood in the ventricles. As a result oxygen content of blood flowing to the different organs of the body is reduced. This leads to blue color (cyanosis) and these babies are called ‘blue babies’.