if you just started walking this could be normal until your body gets used to the new exercising. however if you are very active and are having a great deal of discomfort you should see your doctor. the feeling of your heart as if it is being held or squeezed is not a normal reaction that doesn't mean it's serious or life threatning by any means but it certainly means you should consult with your physician. at only 14 yrs of age you should not be experiencing this and if you are saying this occurs with only walking a very short distance you really need to see your doctor.
after walking a short distance my heart beats very strongly as if i just ran occasionally with lightheadedness included. my heart also not exactly hurts but feels as if it's being held or squeezed. almost like if you fully exhale and stick out your stomach and you feel a pressure in your chest. this is a constant discomfort and has been for about three days. i am 14 female and i get regular exercise. i'm hoping it's nothing serious.