Adults with congenital heart disease represent an increasing population of patients that require repeated surgical interventions, most commonly for pulmonary valve replacement (PVR) and stenting [1]. Currently, the decision for treatment relies on symptoms, including arrhythmias and abnormal right ventricular volume and function [2], however the optimal timing for surgery remains unclear [3]. The aim of this work is to investigate the altered haemodynamic environment of the pulmonary bifurcation in adults with repaired tetralogy of Fallot, before and after pulmonary valve replacement. The overall objective is to derive a computational fluid dynamic metric to determine the optimal time for surgery. In this preliminary study, we present results in simplified geometries of the pulmonary trunk, focusing on the effects of geometry and flow conditions