Hi, I'm a pretty healthy 17 year old girl, but lately my heart has been racing just by walking across the room. I run cross country, play soccer, and run track, so physical activity is something I do on a regual basis. This morning I walked over to one side of my house and my heart rate felt like I ran three miles. When I would breath in all the way my left upper part of my chest would feel tight, but not a stabbing pain..(Like if someone was givving a reall big hug in one area!) I was scared so I called my mom and she is a nurse so she told me to take my pusle for 15 seconds. I did and it was 140 (35x4). This is obviously a problem because my base line is 60 and if I just walk around it should go anything over low 80's. The only way my heart rate would go down is if I were to either sit or lie down. My parents came home and checked me over to make sure I wasn't lying. After that we went to the ER and was checked in. My vitals were all normal-blood pressure, temp, etc. After that I was seen by an ER doctor and was told that I would recieve an EKG, blood work, urine work, and more blood pressure tests. All my blood work turned out complete normal-Potassium, Magnisium, and sodium were all fine. I was sent home with a holter heart moniter. For somereason the doctors did not seemed impressed by my stories of how my heart should race by such little physical activity. I would know anything for many weeks, but I need to get better before cross country season begins! Help!