What should I expect from first cardiologist appointment?

Hello! Sorry for a long post and possible dumb questions. I’ve just been down the “nobody knows what’s wrong with me we just know somethings wrong” road before and it’s stressing me out to be here again. I want to be more proactive this time. I am seeing a cardiologist next month. I was referred by my endocrinologist because he noticed my heart rate is consistently high at my visits and I mentioned I get dizzy often. I had never paid much attention to my heart rate and had kind of written off the dizziness as a dehydration issue or medication side effect. However, now that I’ve done some research and reflection, I do believe I have POTS. My appointment is still a few weeks away but I have a few questions about what to expect and how to advocate for myself. When the appointment was made, it was for general tachycardia. Would it be more fruitful to call or message ahead of time to let the Dr. know I am looking to specifically discuss a POTS diagnosis? Is it better to go in and see what he says first? Is the cardiologist the person to make that diagnosis? Are there tests he will be able to do that day, or will I have to make another appointment? I made this appointment back in December and March was the soonest I could be seen. I’d hate to wait another three months but I know that’s how healthcare goes a lot of the time. I have already done a Holter monitor (showed tachycardia and some spikes in heart rate) and an ultrasound (came back fine). What do next steps look like after this appointment or after an eventual diagnosis? As the appointment gets closer, I’m feeling more anxious about the unknowns of it all. Especially since my other tests did not really give me any new information. All this to say, I don’t really know what to expect from this appointment, but I want it to be productive. Any advice welcome and appreciated!!