Nervous Nancy Over Here! Heartbeat at 142??

Rebecca
First miracle baby over here super excited!! We had some complications but little bean is good to go!!! 
My question to you is: What is normal heart beat at 7 weeks gestational? Our little bean measured at 142 and the tech said its low. I'm wondering what that mean exactly? Does the heartbeat rise as they get a little older? I'm wondering Bc a friend of mine miscarried at 9 weeks and hers was coincidentally at 142 as well. Thank you ladies I appreciate it.