Working in a Cardiothoracic Stepdown right out of school was the best decision I could have made. It forced me to learn (quickly) and become comfortable when things go wrong; hopefully you will have the same experience I did.
As far as nurse to patient ratios we are 1:3 or 1:2 if we have a pediatric lung transplant. Our types of patient's include pre and post op heart's (bypass, valves, aneurism repairs), post op thoracic cases (wedge resection, lobectomy, esophagogastrectomy, etc.), adult heart and lung transplants (heart/lung or heart/lung/liver is becoming common) as well as pediatric lung transplants and VAD's. On occasion we will have medicine patient's but more often than not they are cardiology or EP.
If you don't already have it, I would recommend getting ACLS certified if it isn't a requirement.
As far as workload is concerned, it is tough. Once you get comfortable with the patient's you will gain a better idea of how to prioritize your day. Ambulation and pulmonary toileting are key to a successful recovery and there can sometimes be resistance with patient's who don't want to ambulate.
Familiarize yourself with the hospital policy's regarding A.Fib, Aspiration Prevention and Swallowing, Blood Product Administration, Chest Pain, Chest Tubes, Enteral Tube Feedings, Groin Bleed Management, IV Drips, Pacemakers, Pain Management (including PCA's and Epidurals), D10, Skin Care/Pressure Ulcer Prevention and Tracheostomy's.
Review Hemodynamics, Fluid/Electrolytes, Dysrhythmia's, ABG's and if you have transplants you should be familiar with what medications NOT to give in a code.
Finklemeyers Cardiothoracic Surgical Nursing is a book that has been very helpful in expanding my knowledge of patient populations.
As far as medications to know make sure that you ask that when you start orientation. Every facility is different in what medications they take out on stepdown unit's. Definitely read up on pressors and inotropes.
Hope that helps and may you love your job as much as I love mine!!