I'm gonna be honest with you, you will be in the same world of very critically ill patients but on completely different ends of the spectrum. You are already familiar with end of life and comfort care which can be a very big part of Critical Care Nurse, but it will be a very intense transition.
It's going to be fast paced, stressful, scary, but fun all at the same time. Make sure to study up on your A+P and your pharmacology especially when it comes to cardiac meds. Ask lots of questions and write everything down because you will be thrown a lot of information in a very short amount of time.
You will also have to work on your time management, organization, and your critical thinking. The Units are very fast paced and you need to be sharp as a tack. It can be very overwhelming but also amazingly fulfilling. You are on a career path that is not the USUAL recipe for Unit nursing but if you are willing, have the hunger, and drive to learn and to better yourself, then you will be great!
Congrats on the new gig!