Tetralogy of Fallot symptoms vary, depending on the amount of blood flow that's blocked. Signs and symptoms may include: 
A bluish coloration of the skin caused by low blood oxygen levels (cyanosis)
Shortness of breath and rapid breathing, especially during feeding or exercise
Poor weight gain
Tiring easily during play or exercise
Irritability
Prolonged crying
Heart murmur
Fainting
An abnormal, rounded shape of the nail bed in the fingers and toes (clubbing)
 Tet spells Sometimes, babies who have tetralogy of Fallot will suddenly develop deep blue skin, nails and lips after crying or feeding, or when agitated. These episodes are called tet spells. Tet spells are caused by a rapid drop in the amount of oxygen in the blood. Tet spells are most common in young infants, around 2 to 4 months old. Toddlers or older children might instinctively squat when they're short of breath. Squatting increases blood flow to the lungs.