I have worked in Elecytrophysiology for the past two years and was looking to get certified in cardiac/cardiovascualr Nursing. I find there are 2 different Boards to get certified.
The American College of Cardiovascular Nursing:
http://gpsmoves.com/accnindex.html
For this certification there are 5 different levels. You do not need to have a SBN to take the first couple of levels but you need a masters for some of the other levels. They also differentiate between areas like MICU, non-acute, etc.
American Nurses Credentialing Center:
www.nursecredentialing.org
ANCC differentiates between BSN and ADN and has two different exams. If you take the ADN exam you get to use RN, C which stands for 'certified'. If you have a BSN you use RN, BC which stands for Board certified.
These are the credentials the 'Magnet status' hospitals encourage. You get a discount if you are a member of the American Nurses Association.
CCRN is for Critical Care RN and does not require a degree but encompasses more than just cardiac nursing.