I would also recommend brushing up on your pathophysiology regarding not only general ICU conditions, but Cardiac specific conditions as well (i.e., Acute MI, Cardiogenic Shock, PE, CHF, DVT, Airway Management, etc.). I have always found it helpful to try to break down the patient's disease process in order to anticipate what the needs of that patient are at that particular moment & what possible adverse events could occur. Also, don't feel disappointed if you feel that you are not "catching on" to things or if you feel that others are smarter & more prepared than you are. I have worked in CVICU for over 2 years now and I still learn new things about disease processes & management every day. I agree with Biff that you need to understand normal lab values & x-ray results as well. The best advice I can give to you is to be interactive with your providers to understand the provider's rationale & stay motivated to learn as much as you can. If you have an Itouch or Iphone, some apps I have found helpful have been Medscape (provided by WebMD) and Libermann's Radiology app. Both are free (last time I checked) & they provide useful insight & study tools for drugs, disease processes & management, labs, & assessment findings.
Good luck with your career in the CVICU!