Some tips:
1. Look-up the research interests of the faculty before your interview and indentify a potential mentor.
2. After you are e-mailed your schedule, ask to meet with that potential mentor if you are not already scheduled to do so. You should also ask to meet with anyone who shares your specific clinical interests. For example, if you want to do interventional, ask to meet with the head of the cath lab. The programs are usually pretty good about setting you up to meet with like-minded faculty, but this isn't always the case. The reason to do this is that you want to get as many people on your side as possible.
3. You should be be prepared to give a sales pitch. "I want to be an academic general cardiologist with a focus on prevention who does outcomes clinical research. I have done research on "x" in the past and I have an idea to study "y". This is ideal because Dr. "z" is already studying "whatever", which is similar to "y" and he would be a great mentor. I am scheduled to meet with Dr. "z" later today to discuss some of my ideas"
4. If you are applying to an academic program, be familiar with what type of funding is available, F grants, K grants, AHA grant, etc and which you would be eligible for. But don't bring it up and less you know exactly what you are talking about.
5. Make sure your sales-pitch makes sense and is conguent with your application. Don't say that you want to do interventional cardiology and you plan to apply for an R01 during your last year of fellowship. That is unrealistic...very few interventionalists have an R01 and they are not available to fellows.
6. Make sure you are friendly with the fellows. EVERYONE is evaluating you during the interview day. I have seen applicants get black-listed because they rubbed some of the fellows the wrong way during lunch.