A Few Weeks Ago....felt Like Irregular Heartbeat Especially Early In

a few weeks ago....felt like irregular heartbeat especially early in am & just before going to bed. Since then , occasional very slight sort of pain, in lower left neck area, left shoulder area. Very slight & sometimes think I am imagining it. 64 years old. Couldn't feel any better than i do. No different than when I was 30 years old. Weight the same as I did when I was 30 years old. Full of energy. Play softball 2- 3 times a week. Run like a maniac. No discomfort. Fell tip top. Can run home to 3rd base. No discomfort or short of breathness. Barely breathe hard.