Magnetic Resonance (MR) phase velocity mapping is a noninvasive flow quantification method that is well suited for analysing in vivo blood flow patterns. This talk provides an overview of its role in exploring in vivo blood flow dynamics using 3D flow visualisation and dynamic feature extraction. Different visualisation techniques are examined and their respective drawbacks are analysed. Advances in in vivo flow imaging techniques have made it possible to generate rapidly vast quantities of data which provide relatively comprehensive flow information. It has been shown that it is possible to acquire volumetric cine velocity data in a reasonably short period of time and therefore may become possible to perform such studies routinely in a clinical environment. Before similar advances can occur in our ability to grasp in vivo flow, there is a need for systematic study of three-dimensional time varying flow fields and their diagrammatic representation. This approach of using qualitative topological descriptors assists the understanding of the structure of flow fields and provides a reference for interpreting the numerical results. This talk also highlights future developments in MR flow imaging and the complementary role of computational fluid dynamics that may provide further insight into the genesis and development of cardiovascular disease.