Patients with Fontan-operation, single-ventricle heart frequent have systematic collaterals that increase pulmonary blood flow. The competitive flow elevates pulmonary artery pressure, a process leading to erosion of flow energy. We developed a novel post-processing of 2D cine MRI named for “vortex flow map” to evaluate the energy-loss in Fontan-circuit. Vortex flow map shows energy-loss as small magnitude of vortex flow (MVF) and reveals the relation to heterogeneous pulmonary perfusion. In total cavopulmonary conversion, 4D flow can visualize energy-loss caused by a meandering extra-cardiac conduit and the conflict flow, leading to reduce unilateral lung perfusion.