What Causes Rapid Heartbeat And Pain In Chest With Normal Tests?

I ve been to the era ten time and always vitals are fine other than rapid heartbeat. Twice near 200 bomb. Now for 24 hours it s been sustained between 105-115 and I have pain in my chest and back. I tried to get up but made it maybe ten feet and fell to my knees and had to crawl back to bed. Cardiologist says my heart is fine but I am getting worse every day.