To assist in surgical planning, we simulate the flow of blood — known as computational fluid dynamics (CFD) analysis — for patients who have complex single ventricle heart disease. We use this tool to predict many important aspects of a planned Fontan surgery, including distribution of blood flow to the lungs, how to minimize energy loss, and which Fontan option is best for the patient. Each patient has different surgical options planned on their individual anatomy; these can be evaluated with simulation before surgery. These simulation tools help us maximize the efficiency of blood flow and better understand the risk of blood clot formation after the Fontan procedure.