Slow fetal heartbeat 6 weeks? Worried

Caroline
Hi everyone,
After pain and light bleeding I've just come from a transvaginal scan
Baby where it should be bloods ok
But very faint heartbeat
They sounded very negative and said it should be beating strong for its size now and it isn't 
I'm going for further scan in 10 days so they will know then either way
Any of you come across this before? X