That's pretty much correct. There are some residency programs that require you to do a year of either preliminary medicine or preliminary surgery, or a transitional year. What this basically means is that you have to do a medicine or surgery internship before you start training in the field of your choice. You may do a preliminary year at the institution that you will be continuing your training in, or you can do it somewhere else. From what I understand, a transitional year is basically like glorified med school (with responsibility) -- you do a mix of a whole bunch of specialties, including surgical as well as medical.
Examples of programs that require this are some EMed programs, radiology, ophthomology, dermatology. Cardiology does not fit into this category -- you have to do a full 3-year internal medicine residency, then you do a 3-4 year cardiology fellowship after that.