Figure 5.

Change of restriction by the bottlenecks in the Fontan circuit: circulatory failure with ‘preserved’ ventricular function. Normal flow at rest in normal human and minimal output to remain functional is indicated by the orange lines. The restriction of the two dominant bottlenecks in the Fontan circuit is depicted: (a) the Fontan portal complex FPC (blue) and (b) the ventricle (red). Height of the bottleneck reflects its restriction: the lower the more restrictive. Flow through the circuit will be determined by the most restrictive bottleneck. Early on, the ventricle is able to pump more flow than provided by venous return. Immediately after establishment of a Fontan circuit, the FPC is the most restrictive and thereby becomes the main controller of flow and congestion. Ventricular function is not restrictive (good cardiac reserve and extra‐cardiac operation) at the start, but may gradually decrease for various reasons. Over time, restriction related to FPC increases resulting in decreasing cardiac output; the FPC remains the most important determinant of cardiac output. Once flow reaches below a critical minimal, the circulation fails and demise ensues