Central illustration.

Schematic showing the relationship between pulmonary vascular reserve and end-organ function. Pressure-Flow relationship showing change in mean pulmonary artery pressure (Fontan pressure) per unit change in cardiac output during exercise. Abnormal pulmonary vascular reserve defined as mPAP/CO slope >3 (red) is associated with worse endothelial dysfunction and end-organ dysfunction (more liver stiffness, renal dysfunction, volume overload and exercise intolerance) as compared to normal pulmonary vascular reserve defined as mPAP/CO slope ≤3 (black). mPAP/CO slope: change in mean pulmonary artery pressure per unit change in cardiac output