**2.2 Fontan anatomy**

The systemic venous blood passively entering the pulmonary circulation through a total cavopulmonary anastomosis (TCPA). Blood bypasses the right atrium via a baffle or a conduit. Blood is oxygenated in the lungs and enters the pulmonary venous system reaching the left atrium. The right and left atrium now function as a common pulmonary venous atrium (CPVA). A single functional ventricle actively drives blood flow through the systemic arteries and capillaries, with systemic venous return passively entering the pulmonary circulation. The final Fontan stage results in the conversion of a parallel circulation to a pulmonary and systemic circulation that is in series [2, 5] (**Figure 3**).
