Ok. So... You have had had all relevant tests and nothing was found.
This means that nothing is wrong with you.
The things that you fear being wrong have been PROVEN to not be a possibility for you.
Write this down and repeat it to yourself.
Your obsession over you heart (and yes, this is now an obsession,) has become habit. You have now fully trained yourself to think about it 24/7, check for signs that there is something wrong 24/7 and to then monitor yourself 24/7.
This is now so deeply ingrained in you that it is going to be hard to break the habit... But break it you CAN.
Therapy can take a while..there is no set time. The important components to therapy are that you have a good therapist (this may sound obvious but so many don't.) you need to truly be able to click with your therapist and for them to understand you.
Secondly, you need to be 100% truthful when you see them. Again this may sound obvious but you would be surprised at how many people with old things because of sheer embarrassment alone.
Another thing I will say is this: yes, your BP alters (sometimes dramatically,) when you are stressed.
I don't mean this nastily - but think... Do you really expect for your body to experience severe anxiety and panick and for it NOT to show signs of elevated stress?
You are not a machine. Yes, your body will respond. Your body responding to stress is not your issue, nor is your elevated heart rate despite being convinced that this is the problem....
No. Your problem seems to me that you are frightened of your own body...frightened of what it can do/can't do... Frightened of being out of control.
This is what you need to focus on.
stop monitoring your BP and heart rate... Even if just for one day.
You don't need to monitor it..imagine all the people in the world and all the vigorous exorcise that some do, do you think they constantly monitor their heart? No.... Because they don't fear their body.
You need to let go...break this habit...accept your anxiety and acknowledge your obsessions. Believe in your diagnosis...and stop self diagnosing. It's hard...but with time you can do it.