Cardiac catheterization is an invasive albeit common procedure performed in children with congenital heart disease for intrathoracic oxygen saturation assessment, exposing patients to anesthesia and risk of infection and complication. Prior MRI based intrathoracic oximetry methods have been limited due to partial volume contamination of the blood pool with surrounding tissue and motion corruption. Recently, subtractive MRI oximetry methods have demonstrated reliability and robustness but are limited to Cartesian strategies in the brain[1, 2]. In this work we use a subtractive, velocity encoded, non-Cartesian rosette trajectory for quantitative, motion robust, extra and intravascular flow and T2* mapping entitled Multi Echo fLowencoded ROSEtte (MELROSE). We validate flow and T2* values in a flow phantom and present preliminary results in a healthy subject.