Tetralogy of Fallot (fuh-LOE) is an uncommon condition consisting of four ( tetra ) defects within the heart structures of infants and young children. Together these defects cause reduced blood flow to the lungs and mixing of blood from both sides of the heart. Signs and symptoms of tetralogy of Fallot vary, depending on the extent of obstruction of blood flow out of the right ventricle and into the lungs. Typical signs and symptoms may include: A bluish coloration of the skin caused by blood low in oxygen (cyanosis) Shortness of breath and rapid breathing Loss of consciousness (fainting) Clubbing of fingers and toes (an abnormal, rounded shape of the nail bed) Lack of appetite Poor weight gain Tiring easily during play Irritability Infrequently, babies with tetralogy of Fallot will suddenly develop deep blue skin, nails and lips after crying, feeding or upon awakening. These episodes are called Tet spells and result from a rapid drop in the amount of oxygen in the blood. Toddlers or older children may instinctively squat when they are short of breath. Squatting increases blood flow to the lungs.