Hi the heart beat should come anywhere between 6 to 8 weeks, did your doctor ask for re scan? See there are 2 reasons for no heart beat 1. Late conception, if your ovulation is delayed say instead of 14th day it happend on 20th day then its called late conception. So your LMP weeks and scan weeks would not match. If that's the case then heart beat should come within a week. 2 . The second reason is missed abortion, due to chromosomal abnormalities the fetus did not survive. So please wait till your next scan, take the tablets and stay positive.