Former Vice President Dick Cheney is recuperating from surgery to implant the kind of mechanical pump now being given to a small but growing number of people with heart failure so severe that they would most likely die within a few months without it.

The pumps are partial artificial hearts known as ventricular assist devices, and they come in various models. Mr. Cheney’s kind is about the size of a D battery and leaves most recipients without a pulse because it pushes blood continuously instead of mimicking the heart’s own pulsatile beat. Most such pulse-less patients feel nothing unusual. But they are urged to wear bracelets or other identifications to alert emergency room doctors as to why they have no pulse.

The pumps are not cures and do not replace the heart. They pose significant risks and are implanted as a last resort either for permanent use or as a bridge to transplant until a donor heart can be found. An estimated five million people in the United States are in various stages of heart failure. Patients in end-stage heart failure are severely short of breath, able to walk only a few yards at a time, or confined to a chair or bed.

As a small number of published studies have shown increasing success with the devices — which are powered by batteries that are about 4-by-6 inches and are connected by a wire that goes through the skin — leaders in the field are trying to increase public and physician awareness that such therapy is available and relatively safe if the patients are carefully chosen. Current belief is that the best time to refer patients for such therapy is before kidney, liver and lung damage develops.