NCIt definition : A syndrome characterized by the reversal of a septal defect-associated left-to-right
shunt due to the resulting secondary pulmonary hypertension. The presence of the pulmonary
hypertension causes increased pressure in the right heart chambers resulting in the
reversal of the shunt into a right-to-left shunt. Signs and symptoms include cyanosis,
pulmonary hypertension, heart failure, and high red blood cell count.;