Babys heartbeat (is it normal)

Today I had an ultrasound at the e.r and Dr said the baby's heart beat of 170 was to fast but i was so confused because I thought 170 was good. Anyways I was cramping that's why I went to e.r and after I was sent home I started bleeding with brown blood mainly when I wipe.. I'm 10 weeks 6 days obgyn said maybe a miscarriage but didn't say anything about the heart beat being to fast soo I'm confused.. What was your baby's heart rate at? Praying I'm not having a mc trying to have hope sense there was a heartbeat but Dr seemed like a downer and didn't even let me see the screen or tell me much ugh