Newborns with single ventricle physiology are usually palliated with a multi-staged procedure. When cardiovascular complications e.g., collateral vessel formation occur during the inter-stage periods, further treatments are required. An 8-month-old patient, who underwent second stage (i.e., bi-directional Glenn, BDG) surgery at 4 months, was diagnosed with a major veno-venous collateral vessel (VVC) which was endovascularly occluded to improve blood oxygen saturations. Few clinical data were collected at 8 months, whereas at 4 months a more detailed data set was available. The aim of this study is threefold: (i) to show how to build a patient-specific model describing the hemodynamics in the presence of VVC, using patient-specific clinical data collected at different times; (ii) to use this model to perform virtual VVC occlusion for quantitative hemodynamics prediction; and (iii) to compare predicted hemodynamics with post-operative measurements. The three-dimensional BDG geometry, resulting from the virtual surgery on the first stage model, was coupled with a lumped parameter model (LPM) of the 8-month patient's circulation. The latter was developed by scaling the 4-month LPM to account for changes in vascular impedances due to growth and adaptation. After virtual VVC closure, the model confirmed the 2 mmHg BDG pressure increase, as clinically observed, suggesting the importance of modeling vascular adaptation following the BDG procedure.