I was sitting writing an email at my desk when I felt my heart start to beat really hard. It didn t beat any faster than it already was, just hard, like it was knocking on my chest. It wasn t like when i had run out of breath but rather like someone was flicking at my chest from the inside. It went away after about 6 seconds. I was just wondering what could have caused it. I m 5 10, 208lbs and I m a heavy smoker. I ve never experienced it before. I ve done a few fun runs, I ve done meth but I ve never felt my heart beat that way before. Also, I did not change anything in my daily routine that day.