Little is known of baseline anatomic, hemodynamic and fluid dynamic cardiac magnetic resonance data in single ventricle patients immediately after Fontan. A comparison from that timepoint to the teen years can demonstrate clinical course, potentially predict future events and may shed some light regarding how to optimize outcome. This cross-sectional study is meant to characterize these parameters from just after Fontan to the teenage years.The anatomy, flows and computational fluid dynamic modeling of 22 patients 3-9 months after Fontan (age 3+1.1 years) and 25 teens (age 16+1.8 years) were compared. Significance was P<0.05.The % Fontan pathway stenosis was greater with cardiac index, fenestration flow and caval return lower in teens than younger patients (for Fontan pathway stenosis, 43% vs 21%, P=0.009), however, hepatic flow distribution (HFD) was more evenly distributed in older patients. Pulmonary artery size kept up with somatic growth. In the teen group, indexed powerloss (R=0.39), % Fontan pathway stenosis (R=0.62) and particle resident time (PRT) (R=0.42) deteriorated as time from Fontan increased (P<0.04 for all).There are mostly aspects of deterioration with a few bright spots of stability in anatomy, blood flow and fluid dynamic parameters in Fontan patients from the post-operative period to the teenage years. Most notably, Fontan pathway stenosis increases with decreasing flows while pulmonary artery size and HFD remain stable or improved. These data may be aid in designing improved Fontan reconstruction to optimize clinical outcome and to understand future complications.