I am 6 weeks pregnant, no heart beat found on intravaginal ultrasound. baby measures 7mm. hcg levels are good. should i worry?

Follow up is needed: Normally, if an accurate measurement performed by a certified skilled sonographer is that the embryonic pole is greater than 5-6 mm but cardiac activity can not be detected, there is an increased probability of an "early pregnancy loss". HCG reflects trophoblastic/placental development but not embryonic or fetal condition. A repeat sonogram should help answer your question.