Although viscoelastic flows are characterized by a very low Mach number regime, it involves a weakly compressible liquid phase, which requires a special treatment. This work is devoted to the mathematical modeling and numerical simulation for viscoelastic fluids. It follows directly a previous publication, PhD dissertation of the author. A Unified purely hyperbolic mathematical model for compressible and incompressible viscoelastic fluids is presented. To complete the mathematical model, a complete chapter is devoted to describe a new procedure to determine the correct type and number of boundary conditions for hyperbolic systems. Then a new model describing the non-isothermal viscoelastic flows is introduced while keeping the hyperbolic nature of the system. The main advantage of the proposed model over the existing ones is its hyperbolic nature, which overcomes some of the drawbacks of the available models. The proposed model is then solved numerically using a hybrid finite element/finite difference scheme.