Know your rhythms! Are you familiar with them? I know med-surg nurses typically do not deal with tele monitors. See if your institution offers an arrhythmia course. If not, I recommend either ECGs Made Incredibly Easy or ECG Workout - both books are excellent.
Regarding rhythms, know your heart blocks! Here is a cute little mnemonic I learned:
If your R is far from your P, then you have a 1st Degree (prolonged PR interval >0.20sec)
Long, longer, drop...then you have a Wenckebach (Second Degree Type 1)
If your P's don't go through, then you have a Mobitz II (Second Degree Type 2)
If your P's and QRS' don't agree, then you have a 3rd Degree.
Be familiar with cardiac drugs, drips (Cardizem, Amiodorone, etc).
I work in progressive care, but it is essentially a cardiac/telemetry step-down. We get A LOT of chest pain/NSTEMI/post-intervention STEMIs, angina, pre & post-cath patients, CHFers, HTN, rhythm disturbances, patients undergoing pacemaker/AICD placement, etc. We also get other patients with other primary diagnoses, such as SOB, pulmonary edema, COPD, DKA, ARF, etc, but they have an underlying cardiac history that requires closer monitoring.