How do I not get so tired in cardio?

How long (weeks, months) does it take before cardio exercise gives results?

• I've had some problems with a high resting pulse (120-150) because of anxiety, but now my resting pulse is normal (between 60-77, usually). When I get up though, my pulse usually shoots to about 80-90, and now (and I don't know if this has something to do about anxiety *as well*) when I measure my pulse when walking and moving at the same time my pulse goes all the way up to 130. I don't get tired, dizzy or breathe heavy, but my heart just beats really fast. I'm only 16, but I'm really overweight. I've had an ultrasound done, chest x-ray, lots of blood tests and ekgs, and everything's fine. I'm gonna start doing cardio and eating more healthy, but when can I expect to see results? I don't want my pulse to get so high so easily, so I'm just wondering how long I should do simple exercises (like these http://www.active.com/fitness/Articles/11-Fast-Cardio-Workouts.htm) before I kick it up a notch.

• Answer:

  2 weeks (its a scientific fact!) . Take a before pic today and one two weeks from now. You will see your results :)