Chest Pressure and left arm tireness when exercising

[PenOfDen]

I've been running since 1970 and long distance running since 1994 to present.
I train to run the NYC marathon in Nov, every year. I'm not fast and my time is 5 hours.
I'm 64, 5-8, lbs and I've always been healthy. The first time I experienced the chest
pressure was June 2011 at about 1 mile into a run. I stopped, walked and felt better, and then I tried running again
and stopped again with the chest pressure. I thought I was having a heart attack.  I went home took my blood pressure and it was fine. For the next few weeks I would try jogging and would get the chest pressure.  I finally went to the Dr and took an EKG, chest x-ray, blood work and 3 breathing test.  All were OK.  I started walking at about 14 minute miles, which is a pretty good walking pace.  I typically run 9 to 10 minute miles.  No problems walking, even up to 3 hours.
I have tried wearing a heart rate monitor and keeping my pulse between 120 to 140 bpm and working my way up to
running 3 miles.  I can do 6 miles, if I walk and jog for about 1 hour and 20 minutes.
I've searched the internet and can't find my symptoms from exercising.  
I've been trying to build up my endurance for 5 months, but I'm not able to get over the chest pressure kicking back in at about 2+ miles.
I've never experienced anything like this before.  I really want to run a marathon in 2012, but the chest issue
needs to go away.  After 15 marathons since 1994 I have a pretty good idea how my body handles stress of long runs.  Hopefully, someone has gone through the same thing and can tell me what they did to over come the problem.

Thanks for reading and sending me your suggestions.
Remember, I've already seen 4 different Doctors and have not found the answer yet.

PenOf Den

[black_cat1010]

even though your tests were normal, it still sounds like a heart thing. especially because the problem happens specifically on your left arm...if it is a heart thing, than changing your diet could help. why don't you make a few simple changes to see if it helps? what's your diet like right now? this problem could be a bad heart, even if it's not as severe as a heart attack. in which case, toning down your workouts for a little while until you heal your heart might be a good idea.

[TerryTeeJay]

It would not hurt to even have the disc's in your neck checked.  I have a problem with c6 c7 and have the same problem.  x rays and mri should be able to see if it is in your neck.

Best of luck