My dad is a cardiologist and he told me 200 - 400 beats is when you should be worrying. Rapid heart beats are totally normal for anxiety. I get them all the time! There's a great breathing exercise you can use when you feel your heart begin to race, and it'll help slow you down!
It's called the 4-7-8 method. It's really helped me calm down. I dunno if I can post links here (is that allowed?) but you should be able to find great videos on it if you google it. Also, chamomile tea slows me down and calms my fears. That's always worth a try for you!