If you are considering doing an IM residency (which it sounds like you are based upon your interest in GI and cards), a VERY worthwhile elective would be to do a month of Critical Care (e.g. in the ICU/MICU/whatever). Do so in a "closed ICU" that has its own unit team versus an "open" ICU, where anyone can admit. It is literally a living physiology laboratory. It really will help you take care of the far end of the disease acuity spectrum. There is also (depending on where you train) a tremendous opportunity for procedures (e.g. chest tubes, central lines, A-lines, possibly doing intubations, and of course, ACLS protocols).