21.   But artificial hearts still fall far short of their living models, and no one knows that better than their designers.

22.   But because of a severe shortage of donors, surgeons are testing self-contained artificial hearts and other mechanical devices to keep patients alive until donor hearts become available.

23.   But he suffered a debilitating stroke soon after receiving his artificial heart.

24.   But that artificial heart looks too darned real, making me acutely aware of my mortality.

25.   But the Louisville surgeons operate on many other patients and have to clear blocks of time in their schedules to implant an artificial heart.

26.   By having his own heart removed and being placed on the artificial heart system, Corbet has been moved up on heart transplant list.

27.   But which humans should be the first to receive the new artificial hearts?

28.   Congressional pressure assured continuation of the program largely because of the number of people who might benefit from an artificial heart.

29.   Daschbach cited as examples the creation of the atom bomb, and the development of medical ventilators and artificial hearts to sustain human life beyond its natural boundaries.

30.   Designing an artificial heart seems like a straightforward engineering problem.