5 week ultrasound

Amy

According to the date of my last period, I should be 6 weeks along, so they set my first appointment for next week. But I have long cycles and I think I ovulated late so I think I am only 4 weeks along and will only be 5 weeks maybe 6 at my appointment. What will they see/Can they hear a heart beat at 5 weeks? Should I see if they will push it back a few weeks? Thanks!!