Total Artificial Hearts (TAHs) could be used as an alternative to heart transplantation for patients with terminal heart failure. A fully implantable TAH is under development at our institute. Some critical aspects in TAH development are a) sufficient cardiac output, b) adequate left-right flow balance, c) measurement and control of pump performance and d) hemocompatibility. In this paper, the results of the validation process including in vitro, acute and first chronic in vivo experiments are presented.