I'm a 35-year-old male, non-smoker, who has been training for a triathlon for about 12 weeks, and running and exercising for years. Aerobic capacity seemed to be steadily improving. A few weeks ago, I increased the intensity of the exercise. After riding the bike for about an hour, I started to run and could not catch my breath. Two days later, I experienced the same thing only minutes into my swim workout. Since then, I have had tightness in my chest and the feeling that my heart is beating harder than normal. This feeling seems to be slowly improving but I still feel short of breath at times. I went to doctor who conducted BPM, blood pressure, and EKG, all with normal results. He has recommended Holter monitor because of lone incident of atrial fibrillation one year ago. Cardiologist at that time attributed it to stress and caffeine. (Now caffeine-free). I have checked my pulse regularly and know this is not a-fib. Have an appointment tomorrow to check for EIA, which I was diagnosed with in high-school football but have had no symptoms since. Only thing that doesn't fit asthma is that I'm not coughing or wheezing. Am I on the right track? Any suggestions? Triathlon is in 5 days and I'm still hopeful I can participate. Thanks.