Hello a perfect circle and happyfamily6: couple of thoughts.
Check your BP.
For me there was a correlation between BP and a beating heart. Reducing carbs and protein eliminates the beating for me and upping exercise also removes it. So for me it is probably arterial inflammation caused by excess carbs and protein. The exercise is better with an endurance component rather than HIIT. I can directly correlate the BP/diet and exercises with the beating.
I use these heart herbal therapies: Cayenne, Hawthorne - all components, and lecithin - all in my foods if possible. I make sure my minerals are in good supply: K, Mg, Ca, Se and am aware of Cu Zn and Iodine. Again all food sourced.
For me those things work but that does not imply that they would be successful for you. A friend took four years to beat the beating and reduce BP. Patience also part of the picture. T2