Al,
Three places in Cincinnati proper come to mind: Christ, Jewish and Bethesda North. You've already got opinions about Christ and Jewish. I've used Bethesda North several times, and that's where I had my recent AVR and pacemaker implant. I had a great experience there: Bethesda's cardiovascular program is a little different than Christ and Jewish; Bethesda has a combined ICU/step-down unit for cardiovascular patients (and, in fact, similar units for several other kinds of patients), so I didn't change rooms when I got out of intensive care, and the patient/nurse ratio stayed very low the whole time I was in the hospital. Bethesda's heart surgery center was recently rated "best in Cincinnati", though I'm not sure who did the rating; if you'd like to know, I can look it up.
There are several other Greater-Cincinnati-area hospitals that are closer to Dayton than Christ, Jewish or Bethesda North, but I don't have any experience with them, and I don't know anyone who does. Two names come to mind: Mercy Hospital Fairfield and Middletown Regional. Of the two, Middletown Regional is closest to Dayton, though it's really only "close" if you'll be staying on the south side of Dayton.