Historical and state-of-the-art review of clinical mechanical circulatory assist and replacement devices. Recent clinical experience at the University of Ottawa Heart Institute with various mechanical circulatory assist devices as a bridge to transplant, and experimental results with the development and testing of a new electrohydraulic ventricular assist device, are described in detail. A Medline search of the English literature from 1980 to 1996 was done using the following words: artificial heart; ventricular assist device; and transplantation. Papers were selected to provide both a historical perspective and an overview of the current status and future prospects of mechanical circulatory assist devices and artificial hearts. Since the implantation in animals of the first devices in the 1960s and 70s, there have been astounding improvements in design, available materials and implementation of these devices. Increases in the understanding and management of thrombogensis and immunosuppressive drugs as well as developments in the fields of miniaturization, pumps and power sources will lead to concomitant improvements in these devices. The use of these devices has become an accepted treatment for end-stage heart disease. Additional development and testing is required to address persistent complications in most models if they are to become alternatives to cardiac transplantation. The basis of the future successes is dependent on both technological refinements in the developments of new devices and on continued research into the physiological effects of mechanical circulatory support. However, these devices are used both as a bridge to recovery and a bridge to cardiac transplant and it is expected that they will be used increasingly to provide permanent circulatory assistance or replacement.