no. it is too small to be seen at 6 weeks. i had a similar experience. at 5 weeks and 3 days they only saw a gestational sac but at 8 weeks they saw the heartbeat.
i am agree with kimmery , 6 weeks is too early to see the heartbeat , they usually see it around 8 weeks.
Im 9 1/2 weeks pregnant and we seen the heart beat at 5 weeks 4 days. The heart starts beating during the 5th week, so it may be just to small to see or maybe your not as far as long as you think you are. Some women dont see it untill around 7 weeks. By 8 weeks if the pregnancy is progressing normaly you will definitly see the heart beat. Keep us posted on how your next scan go's. Hope all is well :)