The recent clinical use of a pneumatic artificial heart at the University of Utah has focused attention on the role of blood pumps in the support of the circulation. Pneumatically powered assist pumps are now in clinical trials in patients with profound but reversible heart failure after open-heart surgery; survival rates as high as 50% in a heretofore lethal condition have been encouraging. The results of animal studies with the pneumatic artificial heart suggest that these devices are ready for clinical trials; the major application is likely to be as a bridge to cardiac transplantation. Implantable electric motor-driven assist pumps and artificial hearts are being evaluated in animals as permanent cardiac support or replacement devices; clinical use is projected to begin late in this decade. Initially, these devices will be employed in patients with end-stage cardiac disease who are not suitable candidates for cardiac transplantation or for whom donor hearts are not available. The availability of compact blood pumps will offer new forms of therapy to patients with certain types of profound heart failure.