I thought that all cards fellowships had this, until I went around and started interviewing. At my med school and the hospital where I did residency, the cards fellow is pretty much up all night most nights on call, and definitely is in house. At some programs the cards fellow takes all the chest pain calls from the ER and does all the echos and sees all new cardiology admissions, and at most decent sized hospitals that probably will keep you up all night.
The program I'm going to doesn't require in house call, but it's a bit smaller hospital. I'm expecting to be in there a lot, if not all night. Cards just isn't one of the "sleep through the call night" specialties.