If you are young, like a teenager or young adult, your heart can handle beating that fast for a short period of time, like during exercise and shortly. In a young person your heart rate should come down back to normal within a minute or two after you stop exercising. If your heart rate goes up to 200 without provocation (aka, you weren't exercising, or otherwise exerting yourself to the point that it would need to beat that fast to compensate for your increased activity for a period of time), like while you are watching TV or something, that IS a sign that something is wrong. This can occur from a birth defect, be chemical induced (if you drank/took too much caffeine or some illegal drugs, for instance), or be idiopathic (no known cause). Either way, it needs to be treated. Your heart cannot sustain that rate for long periods of time. Eventually it will go into failure and be unable to support your body. You won't blow a valve or anything, but what happens is this: In between beats (contractions) the ventricles fill with blood. So when your heart beats that fast your ventricles do not have time to re-fill, and therefore push out less blood with each contraction. Eventually, if the rate stays that high, the heart won't be able to pump out enough blood to circulate and perfuse your system. You will be come confused, tired, cold/pale (possibly blue in your extremities), and eventually pass out. Your heart will eventually be unable to keep up it's pace and will stop, either in V-Fib (ventricles are basically quivering like jello - you can shock this rhythm with a defibrillator) or Asystole, otherwise known as Flatline (not shockable). The key is for a health care professional to fix the fast rhythm with drugs or energy (you can shock a fast heart rate like that to try and convert it to a sustainable rhythm. Don't try that at home!! Medics and doctors ONLY!! lol) But, that's basically what will happen. There are lots of other variable symptoms that come with it too, but nothing will "go out," so to speak. And if it's your heart that's beating that fast - go get it checked dude!!!