Why is it that when i ride the j..

Brief：
well, im western, and the saddle is quite hard.when i jog, i bounce a bit when i get into it, but otherwise, i sit it extremely well, better than any .. 

well, im western, and the saddle is quite hard.

when i jog, i bounce a bit when i get into it, but otherwise, i sit it "extremely well, better than any beginner i've had" as my instructor says.

so when im bouncing for a little bit, my chest right over my heart gets sore, like a stabbing pain.

is my heart unhelathy?

im 14 and im not a fat kid, but im not skinny.

im in between and healthy.

wats the prob? wat do i do?

Acid reflux coming up from your stomach being jolted can give pains like that and so can spinal problems. If your spine is out between your shoulder blades, when you sit with your shoulders back or move your arms in a certain way, you can get sharp stabbing pains in the chest. I had them when I sat back on the sofa or swam and once the chiropractor gave me an adjustment, it stopped. It doesn't matter if you are fat or skinny or in between. You seem like you are just not used to getting that type of excersise. Maybe talk to your doctor or slowly walk/jog/ride a bike in your neighborhood until you feel your heart doing that, rest, then try it again. Soon you'll be able to ride longer and your heart will be healthier. I am inbetween also and I have no problems with my heart or breathing because I jogged around my neighborhood (a street or two) then walked, then tried again, and then rode a stationary bike in my house. This is totally normal and happens whenever you haven't been riding often and aren't used to it. Nothing to do with your heart because I'm 15, and weigh about 100lbs and whenever I haven't cantered in a long time it does the same thing. It's just your muscles getting all worked up. Once I started cantering every day it went away, but I know how badly it hurts, so just work your way easily into jogging more and more at a time. My question to you..

Are you wearing a bra that isnt suited to riding? Maybe one that isnt supportive?

It could be that the pain comes from the muscles that are above your breasts are being pulled and leaving you in pain.

Leave the underwires alone for riding too!

Just a thought. To the answer above I hope you are a girl cause that could super offensive, well I haave had pain when riding in the cold weather because of all my chest muscle tightening. If you are tense this could cause this.