I'm sorry you are having this experience. I've had that sensation of racing heart. Like I can't calm down. Honestly, what helps me is to deep breath (breath in deeply for a count of three, hold for a count of three, breath out slowly for a count of three, hold for three, repeat). This is calming to me. And while you do it, visualize something soothing (whatever is to you like a beach, a field of flowers with birds chirping, etc.). Headphones with some calming music or any music really can be distracting. You can practice meditation. I have a hard time with this so for me, I've used the audio with headphones that kind of does it for you. Lazy meditation. :>) Try to exercise because that is not only good for your heart, it's good for stress reduction and lifting mood. And then keep a journal. Write down when you feel this way and what else is going on right before it or during that day. Look for triggers or patterns.
And a therapist may help you explore this a bit as well. good luck
There's a difference between feeling like your heart is racing because of an anxiety attack and an actual heart problem. You apparently don't have a heart problem, at least not according to the docs. Nobody can tell you your docs are right, they're just humans like the rest of us, but given you've got a pretty significant anxiety problem, that's probably the thing you want to work on. And as you say, you don't seem to have adjusted your lifestyle at all to help by not exercising and eating poorly, which will only make things worse. Ever seen a therapist or had any treatment for the problem that is bothering you the most that you know is actually there, the anxiety?