The purpose of this study was to investigate the accuracy and precision of fast plane wave 2-D vector flow imaging (VFI) under laminar and complex flow conditions in a human subject. The method has previously been validated in simulations and straight-vessel phantoms, however, complex flow patterns remain challenging to study, since there are no other imaging techniques accurately enough to compare with. Here, the approach was to study (1) the accuracy by comparing VFI obtained from a patient-specific phantom measurement to computational fluid dynamics (CFD) simulated velocities derived from the same geometry; and (2) the precision in vivo by calculating the standard deviation (SD) of VFI estimates at several evaluation points.