The symptom of the heart pounding and beating irregularly...

Recently, my heart suddenly started beating rapidly, and I was startled.

The symptoms suddenly appeared while I was sitting on the sofa, not even doing intense exercise.

It thumped and rattled loudly enough to hear the heartbeat for about three seconds, and it was running wildly on its own.

I was running so intensely that I couldn't even find a moment to intervene, and then I suddenly stopped.

It was so scary just for a moment.

What could be the early symptoms?

When I had a coronary artery test two years ago, the results came back normal.