Cardiac assist devices are classified into the traditional engineering categories of displacement and rotary pumps. Clinical use and indications of the various pump categories are outlined and a detailed description of the currently available systems is given. The first section deals with extracorporeal as well as implantable ventricular assist devices of the displacement type and is followed by a section on current developments in the field of total artificial hearts. The latter part of the article covers the rotary pump category from cardiopulmonary bypass applications to implantable systems, including specific design aspects of radial, diagonal and axial pumps.