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Patients with tetralogy of Fallot typically present with decreased exercise tolerance and cyanosis due to a right-to-left shunt. Infants and young children may develop hypoxemic spells, characterized by increased cyanosis, hyperpnea and anxiety. Toddlers may squat, a learned response to hypoxemia. Squatting increases systemic vascular resistance and increases venous return to the right heart, both of which improve pulmonary blood flow.