Good question by Christine. I'm 66 and can get my pulse up to the 180's at the end of a long run. It all depends on what you are doing. For me a 143 pulse would be a gentle jog. If your resting pulse is 143, that's scary and any doctor would have caught that in a physical. Try googleing maximum heart rates and you can get a lot of good info. At your age, you should easily be able to get over 200.
What sort of activity have you been up to? Have you taken your temp and BP? Are you having shortness of breath? How long has your pulse been that high? (anything over 100 is abnormal and you may need to see a doctor urgently to see what is going on). Have you talked to your parents?