Tetralogy of Fallot (TOF) is the most common form of cyanotic heart disease and represents up to 10% of all congenital heart defects. The first complete repair was reported by Lillehei in 1954; in the current era most cases are repaired within the first 6 months of life. Although TOF is one of the most successfully repaired cardiac lesions, if left unrepaired mortality in the first several years of life can approach 50%. As with many congenital cardiac lesions, there is a spectrum disease severity in TOF. In patients with uncorrected TOF the anesthesiologist must be prepared to manage hypercyanotic spells and possible associated hemodynamic instability. This chapter details the perioperative assessment and management of an infant with uncorrected TOF with significant right ventricular outflow tract obstruction.