Children with tetralogy of Fallot may develop "tet spells."

Older children will often squat during a Tetralogy of Fallot "tet spell".

Older children will often squat during a tet spell, which increases systemic vascular resistance and allows for a temporary reversal of the shunt.

Tet spells are characterized by a sudden, marked increase in cyanosis followed by syncope, and may result in hypoxic brain injury and death.

Prior to corrective surgery, children with tetralogy of Fallot may be prone to consequential acute hypoxia, tet spells, characterized by dyspnea, cyanosis, agitation, and syncope.