Heartbeat on ultrasound?

Hey, I've just found out I'm pregnant again after 2 miscarriages (one natural, one missed, picked up at 12 week scan, followed by d&c;). I'm currently 5 weeks so very early days. I'm not getting excited, just taking it day by day. I've been told I can have early and extra scans at my hospital but I only want to go when I can see a heartbeat. How many weeks would you recommend I go for a my first scan? thanks ladies :)