Do you know what your maximum heart rate is? I forget the range, but I think it's usually around 200bpm. Really your actual rate will depend on how hard you're working out. Going over 185bpm is probably past your lactate threshold.... for how long can you run at over 185bpm? I dont knnow, but I think if your heart rate was really over working, you should know about it by losing energy, going out of breath, not being able to run as fast, etc... I've never really gotten chest pains like that, in the morning and so painful... though for years I have had periodic chest pain (stinging). For me it's all from acid reflux/heart burn er whatever. It had me slightly nervous for a little while, but then I had my cardio checked and found it was only heart burn.