Your pulse rate could become higher due to taking excercise, becoming excited or scared. If it is persistant however, it could be a symptom of heart disease, thyroid malfunction or emphysema, amongst other things. Get checked out!
There are many reasons for rises in pulse rate. If you are exercising or using allot of energy your pulse rate will go up. If you are suddenly frightened your pulse will go up. If you are excited or...