I second the above.
Apply early, I sent my completed applications in mid February. I did not get any interviews until April however. Ended up interviewing from mid April to late June and got into my top choice program who happened to interview me last on June 28th! So there is no rule about when particular programs are interviewing but I agree, there's a lot of variation. My very good friend made a mistake of applying in late April and her choices were limited.
In terms of application process itself this is what I recommend: first look at each program's website to check the requirements. Then get in touch with the PD or their assistant if there's no clear info on the website. Make sure you have all your paperwork ready, some programs ask for ITE results or copy of your Med School Diploma.
Letters, letters, letters....cannot overestimate the importance of good LORs. Make sure you ask the right people, people who will truly advocate for you. It's helpful if there's someone in your Dept. that is known in cardiac world. Ask if they would be willing to make some phone calls on your behalf.
Also, suprisingly large number of people commented on my personal statement. Apparently they do read these things so make yourself stand out.
Other than that - just be personable, don't try to sell yourself as someone you're not. These interviews (at least from my perspective) are more about who you are, not what you know or have done. You proved already that you are smart, hard working, good anesthesiologist blah blah blah. Now they wanna know if you're fun to work with and have something to bring to the table.
Good luck!