If anyone has any heart concerns go see your GP. Especially if you have a family history of heart issues. I had shortness of breath for a while, put it down to over exertion, by the time I went to see my GP I'd convinced myself it was a chest infection ............... turned out I'd had a series of heartattacks and left myself with Heart Failure (permanent damage to a part of the heart).
I'm back on track - ran 2 half marathons this year and plenty of 5 milers and 10k's but my pace is obviously reduced and a half marathon is the furthest safe distance for me.