1. From Cardiovascular Engineering, Inc (G.F.M.,), Waltham, Mass; Centre hospitalier de l’Universite Laval (Y.L.), Ste. Foy, Quebec, Canada; London Health Sciences Centre (J.M.O.A.), London, Ontario, Canada; Louis Stokes VA Medical Center (M.E.D.), Cleveland, Ohio; Brigham and Women’s Hospital (P.R.C.), Boston, Mass; Erie County Medical Center (J.L.I.), Buffalo, NY.