I'm sure someone will correct me if I'm wrong, but I think most people prefer transcribing for specialties and not acute care so acute care jobs are more plentiful. I think your cardiology experience certainly counts for a lot and there are companies who would hire you for acute care even though that isn't your most recent experience, so apply away and put a comment in your cover letter about being willing to learn or something like that. I haven't done acute care in about 5 years, but from what I remember the trickiest part is all the labs. Sorry I don't have any reference book recommendations for you. Best of luck on your job search!