In Tetralogy of Fallot, the Right Ventricular pressure exceeds the Left Ventricular pressure, resulting in a right to left shunt. Squatting increases systemic vascular resistance which causes Left Ventricular pressure to temporarily rise above Right Ventricular pressure, thereby producing a temporary reversal of the shunt. Therefore, when the patient squats during the cyanotic spells, more blood enters the lungs for oxygenation.
