Congrats on your pg!!!

If there is a heartbeat that is a VERY good sign! Brown spotting is probably just old blood and I would try not to be too concerned (easier said than done) unless you start having some bright red blood and cramping. But nothing is a bigger indicator that things are going well than a healthy heartbeat which you have.

Try to relax and enjoy being pg (again, easier said than done - I am always a mess in my first trimester). Good luck and lots of sticky vibes for you.