Unsteady flow and diaphragm motion in the phoenik artificial heart were studied using a CFD solver combined with an in-house developed FEM code. In diastole, the initially egg-shaped diaphragm deflates and forms two large depressions on the two sides and a small one on the round part. Vortices form in the blood chamber. In systole, the diaphragm inflates and pushes the blood to flow out through the opened outlet. The wall shear stress distribution is also strongly dependent on the flow field as well as the diaphragm motion.