This study called the SNS-PONDER research (Single veNtricle Study: Plethora vs Oligemia on FoNtan proceDurE Result), will investigate the effects of oligemic and plethora conditions in univentricular CHD, an area that has not been extensively explored. As the first study to specifically address this issue, it aims to offer new insights into lung physiology and pathophysiology in CHD patients. By advancing our understanding of these conditions, the study seeks to improve management strategies for patients and enhance clinical outcomes. Furthermore, the findings will serve to better inform patients about their condition and guide in identifying interventions to optimize their care.