I had constant high heart rate and found that my thyroid was hyperactive.
And, also if I ate foods with the preservative, BHT, I nearly had a heart attack, my heart beat so hard!
BHT is in almost all white bread and cereals. I started eating whole grain bread and cereals that don't have preservatives. You have to read the labels!
I hope this helps. It has helped me and gotten me off a lot of medication!