Thanks for raising this question. Let me first distinguish between the medical schools and the clinical training programs like cardiothoracic surgery. Let's take the example of Harvard Medical School (HMS). HMS has a number of affiliated teaching hospitals such as Brigham and Women's Hospital, Beth Israel Deaconess Medical Center, and Massachusetts General Hospital (among others). All three of these HMS-affiliated programs have their own cardiothoracic training programs. The focus and flavor of the programs is slightly different even among the Harvard-affiliated programs. For example, the Brigham program requires several months working on pediatric patients at Boston Childrens Hospital (another Harvard affiliated hospital). So it is not really the med schools, per se, but the teaching hospitals that you would want to look at. In addition, some program are "traditional" while others are "integrated" [https://tsda.org/the-tsda/ct-residency-programs/ct-surgery-training-pathways/]. For ranking, its the same issue as ranking colleges where the same college could be #1 or #5 depending on whose ranking system you are looking at. US News and World report does have a ranking for hospitals but their ratings include both cardiology and cardiothoracic surgery combined in their rankings [https://health.usnews.com/best-hospitals/rankings/cardiology-and-heart-surgery]
