Wow, this thread is totally scaring me. I've had exactly the same path since May of this year and just recently started biking again. At the end of May I took a trip to California and over the week biked around 350 miles. I had the exact same symptoms on my day of return (felt like something was sitting on my chest, couldn't breathe, chest pains).

I went to the ER when I got back, and they did CT scans, X-rays, bloodwork, echocardiogram, EKGs, and kept me overnight. They said I had pericarditis (inflamation of sack around heart). The EKG was the only thing that was kinda off, and that's how they made the diagnosis. They also checked for a pulmonary embolism. I continued to have pain so they thought I had acid reflux and am currently on prilosec 2x a day. They also did an upper endoscopy to see if everything in my upper digestive tract was working properly.

I have recently tried to get back into biking/running, but I have the pain after exercising, but not during. I still have the feeling that I can breathe normally but am not getting enough oxygen in. Did the doctors say why nothing showed up on the ER cat scan? I'm beginning to feel like a hypochondriach since starting having these pains. Chest pains for me are much less now, but still naggingly there. Do you think I should push to see a pulmonologist?