Hey! From personal experience (I am in Division B), the level of difficulty in regionals depends based on the ES you have. Some tests are incredibly easy (the one I had this year had no written response nor diagram labeling!) while others may test you on complex concepts that requires a thorough understanding of the material. As for Andromeda215's questions, you should definitely know about Einthoven's triangle, which falls under ECGs, and creatinine. You should also know what a diuretic is, but I do not know if you need to know the specific types for a Division B regionals test. Again, there is room for fluctuation, but it would be in your best interest to study as much as possible!
And sometimes one should hope for a harder test! If you mess up on an easy exam, it is less likely that you will place as high because other teams probably also found the test easy (I placed 6th in regionals because I messed up on a few questions on an easy test). In other words, harder tests "filter" out the best from the rest and really show who knows the content. All in all, it won't hurt to know more, so study, study, and study!
"Perhaps one did not want to be loved so much as to be understood." -- George Orwell, 1984
Events 2019: A&P, Heredity, Picture This, P&P
Events 2020: A&P, Astro, DG, Geo Mapping