At rest my heart starts to beat strongly for no real reason, the contractions are visually noticeable stirring my body during the beats?

My question is related to heart health. Firstly, sometimes at rest my heart starts to beat strongly without any real reason, the contractions are visually perceptible moving my body during the beats (example: my left pectoral stirs a lot) and I feel each contraction, and this without pain. Secondly, when I do physical activity, I feel my heartbeat in my neck and my head, always without pain and regularly. Thirdly, I regularly feel my louse at the tip of my left index finger. These are relatively new symptoms. Moreover, I am 26 years old and relatively athletic. I've been to the hospital for this before, but after an electrocardiogram, they told me that they didn't see anything strange.