No need to worry about not detecting heart beat at 7 weeks..If a vaginal ultrasound is done and no fetal pole or cardiac activity is seen, another ultrasound scan should be done in 3-7 days. Due to the fact that pregnancy dating can be wrong, it would be much too early at this point to make a clear diagnosis on the outcome of the pregnancy. Sometimes, with normal pregnancies, the fetal heartbeat is not visible until a fetal pole of up to 4 mm in length is seen. Failure to identify fetal cardiac activity in a fetus whose overall length is greater than 4 mm is an ominous sign. It can sometimes be difficult identifying a fetal heartbeat from the background movement and maternal pulsations. And the HCG levels during 7-8 weeks can vary between 7650-229000.. Because of the wide variation in values, the test is not useful in establishing the gestational age of a pregnancy. The hCG levels will peak at about 8-12 weeks of pregnancy and then will decline, remaining at lower levels throughout the remainder of the pregnancy. If the levels are questionable, an ultrasound scan should be used to diagnose the pregnancy outcome. Ultrasound findings are much more accurate at diagnosing pregnancy viability after 5-6 weeks gestation than hCG levels are.. So you can consult your doctor again for an repeat ultrasound scan after 1 week...