Ultrasound shows gestational age 6w4days. Yolk sac present only. Should there be an embryo? Heartbeat?

7 weeks. I usually tell my patients that they should see cardiac activity at 7 weeks . The fetal pole is evident before that. You may want to do beta HCG levels 48 hours apart the change in these values can help answer some of your questions.
Maybe . 80% of pregnancies should have a fetus and heartbeat detected on transvaginal ultrasound by 6 weeks. A repeat exam in 4 to 6 days should help decide if this pregnancy will progress normally. Serial blood tests for beta -hcg are also helpful to detect proper progressive increase of this "pregnancy " hormone.