An analysis of prototyping of embedded Real-Time Systems by means of graphical animation techniques is presented. We analyze the fundamental characteristics of prototyping and their relation to animation mechanisms. We show that animation strongly inherits certain benefits of prototyping while at the same time animation is able to alleviate some of the drawbacks of prototyping. A survey of known visualization techniques for real-time system animation is presented with an assessment to their relative strengths and weaknesses. Finally, the animation approach taken in Esprit project no. 5570, IPTES, is described. Our approach is unique in enabling animation of heterogeneous system models, i.e., combinations of submodels belonging to different levels of abstraction.