Welcome to BB. Like the others have said, brown blood is supposed to mean old blood. I can totally relate to your fear, I had bleeding throughout my pregnancy and it was extremely frightening. I would go to bed and rest as much as possible, it might help you to relax and also make tomorrow come faster. Seeing a heartbeat is supposed to super increase the chances of a successful pregnancy so the fact that you have seen that is a really good sign in my opinion.