Patients with Tetralogy of Fallot often experience "tet spells" which may be caused by crying, fever, and exercise due to exacerbation of RV outflow tract obstruction

Patients with Tetralogy of Fallot may squat in response to cyanotic spells, which decreases right-to-left shunting by increasing systemic vascular resistance (SVR)
inhaled O2 may help stimulate pulmonary vasodilation and systemic vasoconstriction, which can further decrease right-to-left shunting