What Causes Fluttering Sensation On Left Side Of Chest And Low Heart Rate?

Hi, I am physically fit. Run 2 to 3 miles a day just to stay active also use stairs, lift light weight among other activities. I sometimes have or feel flutters on the top left side of my chest (but not when exercising). Non smoker, 133lbs, 5 5 1/2, 52 year old female. I was recently told that my ekg showed a regular rhythm, but low heart rate of 44. Should I consider that normal or any cause for concern? Thank you.