First off, congratulations on your new job!
To prepare, start looking over cardiac diseases. Remember that cardiac patients tend to have other comorbidities as well. Not sure if your unit does drips, but that would be something else to look over, too. On my unit, we can have patients on Dopamine (max is 5mcg/kg/min), Cardizem (max is 15mg/hr), Lasix, Heparin, Dobutamine (but typically these are the ICU transfers and they are being weaned off), Protonix, octreotide, Amiodorone and NTG (we are only allowed to titrate for chest pain, not blood pressure). Look over your cardiac medications and also your EKG rhythms.
Go with an open mind. Ask questions. No question is a stupid question. You've done this before as an LPN, but the role of an RN is different. It's a learning process.
Good luck and keep us posted!