1. From Johns Hopkins Hospital (S.D.R., J.V.C.), Baltimore, Md; Duke University Medical Center (J.G.R., C.A.M.), Durham, NC; University of Michigan (D.B.D., F.D.P.), Ann Arbor, Mich; University of Florida (J.M.A., C.T.K.), Gainesville, Fla; University of Minnesota (A.J.B., R.J.), Minneapolis, Minn; University of Rochester (L.C., H.T.M.), Rochester, NY; and Thoratec Corporation (D.J.F.), Pleasanton, Calif.