Something I considered in deciding whether to apply to UK or UL (I didn't consider it terribly necessary to apply to both) was their success in the Match. From the statistics available from the AAMC, UK has consistently matched all their spots, whereas UL has had some trouble doing so, filling spots in the scramble.
On Cardiology (an area which I myself am interested in pursuing): from what I gathered in talking informally with some of the cardiology fellows, UK used to fill most of their cards spots internally, but things have changed a bit in the past couple of years since they brought in some big-wigs from the Cleveland Clinic who wanted to recruit more "names" (e.g., Duke, UW, etc.). I talked with a cards fellow that is a recent match, and he said it's not impossible to get in as an internal candidate. The keys are probably the same as anywhere: work hard in the CCU, and be nice and get along with everyone. Some people have trouble with the former, others with the latter. The fellow said cards at UK depend a lot on "mid-level" people, like PA's & nurse practitioners, and some residents get a "Dr. God complex" and treat those people like they're inferior, which of course hurts their chances of getting in good with the people you need to do so.
Sorry for the long post, but I hope it helps some.