This is fascinating:

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.