I was working out and suddenly my entire left arm, from the armpit to the tips of my fingers, went numb (as if I had laid on it and it went to sleep ). The tingling/numbness lasted about 10 seconds or so, then mostly subsided, though there is currently some slight degree of tingling remaining (after about 30 minutes of the first onset of numbness). I had no other symptoms such as light headedness, dizziness, or other pain/discomfort. I m 59 years old, routinely workout and am in excellent health/physical condition. I did have open heart surgery when I was 40 years old for a successful mitral valve repair. My biggest concern is, was this possibly a heart attack or could it simply have been caused by something else? Thanks in advance for your assistance. R, Brad