Tetralogy of Fallot (TOF) is a heart defect present at birth where four structures in the heart are abnormal, resulting in deoxygenated blood flowing from the heart to the body. Babies with TOF often appear blue due to the lack of oxygen in their blood. The defects can cause obstruction of blood flow to the lungs. Treatment involves open heart surgery to repair the defects, after which symptoms usually improve. Lifelong follow-up care is important to monitor for complications.