Background: Blood flow assessment is essential to fully understand cardiovascular function in disease pathologies and for identification of individuals at long-term risk of cardiovascular disease development. Qualitative and quantitative assessments of blood flow by imaging modalities have been limited, and much of the accurate quantification has relied on invasive measures.Methods: This review discusses how four-dimensional velocity cardiovascular magnetic resonance (4D flow CMR) offers increasing potential for the non-invasive assessment of blood flow in the heart and major blood vessels such as the aorta. 4D flow CMR refers to phase contrast CMR with flow encoding in all three spatial directions that is resolved relative to all three dimensions of space and to the dimension of time throughout the cardiac cycle. Results: It has been demonstrated that 4D flow CMR can be used to assess parameters such as flow, pressure, velocity, wall shear stress and turbulent kinetic energy throughout the heart and major vessels of the cardiovascular system. It has been possible to gain new insights into cardiovascular pathologies such as, but not limited to, hypertrophic cardiomyopathy, dilated cardiomyopathy, Marfan syndrome and aortic bicuspid valve disease. Conclusion: Future work to standardize 4D flow CMR scan acquisition parameters is required. Furthermore, the development of automated analysis tools and standardized reporting of quantitative metrics are needed to increase capacity for larger studies and for translation to clinical practice. In doing so, the potential for 4D flow CMR to disentangle complex questions related to cardiovascular function will be maximized.