Won't the differences in the numbers and types of required index cases for General Thoracic track necessitate a significant decrease in the exposure to cardiac cases?
http://www.abts.org/sections/Certification/Operative_Requiremen/index.html
Better start studying for Step 1 and cranking out the papers!
I would hope that they don't expect anyone to demonstrate interest BEFORE medical school. Most people go into medical school thinking about one field and end up doing another. This probably arises from the lack of understanding and exposure to the full range of medicine and surgery. My sense, as a medical student, is that it's difficult to wrap your head around any of the fields before you're elbow deep in it, as it were, and the exposure in medical school can be relatively light in some fields... this is probably one of the arguments against early specialization.
Even the Chief of CT at the institution I attend was undecided about Surgery vs. Internal Medicine during his 4th year of medical school! On top of that, the Surgeon-in-Chief at the Children's Hospital told us that he had already matched in Psychiatry before a fateful conversation right before he started his internship sent him off to a gen surg residency and then a pediatric surgery fellowship.
Having said that, a couple of the CT fellows and the congenital heart surgeon who is supervising my research have all said that they knew they wanted to be cardiac surgeons during their first year of medical school.