Cards fellowships, like all fellowships, care mostly about your ability to work as a resident. Therefore, your LOR's (particularly those from cardiology faculty), evaluations from internship year, and your interview will be the most important factors. Other factors include your education background (eg rep of your program), med school performance, and research (it's almost required for many cards programs). Step scores will be sent to fellowship programs, but most don't put very much weight in them. The avg cards resume looks above avg with experience in cards research. Hope that helps!