Large-scale integrated model is useful for understanding heart mechanisms and developments of medical therapy.

In this paper, we discuss the need for a large-scale integrated computer heart model to understand cardiac pathophysiology and to assist in the development of novel treatments through our experiences with the "UT-heart" simulator. The UT-heart simulator is a multi-scale, multi-physics heart simulator that integrates and visualizes our knowledge of cardiac function in various aspects and scales. To demonstrate the usefulness of this model, we focus especially on two problems in cardiac anatomy and physiology. In the first application, the mechanistic implication of complex fiber and laminar structures is analyzed with respect to optimality of pumping performance. In the second application, the coronary circulation is analyzed, to identify factors that determine the behavior of the microcirculatory system. These two examples indicate not only the importance of the integration technique, but also the need to resolve structural complexities of the heart in the modeling. This leads naturally to incorporating high performance computing in medical therapy.