CareCruiser is a system designed to visualize the effects of applying clinical treatment plans and to support the exploration of the effects that the treatments have on the patient´s condition. While considerable progress has been made in recent years concerning the visualization methods to support computer-executable clinical treatment plans, our prototype succeeds in combining and enhancing the possibilities offered by the features of other systems. To ensure the quality of our visualization (1) we collaborated with a medical expert in an early design phase, (2) we conducted a heuristic usability evaluation, and (3) we tested its usefulness with domain experts. In the course of the usability evaluation the evaluators tested the prototype in conformance with generallyaccepted usability principles; in the user testing, physicians were asked to function as users and were interviewed afterwards. Both the usability evaluation and the user testing led to useful results and presented a very positive picture of the visualization and the exploration features of CareCruiser.