Fetal bud 0.4cm without fetal heart may be normal.
Fetal bud 0.4cm is almost 40 days of pregnancy, fetal heart appears almost 6-7 weeks, so no fetal heart at this time may be normal, you can further do a good review.
Generally the embryo development process is 30-40 days to form the sac, 40-50 days to form the buds, 50-60 days to form the fetal heart, so ultrasound needs to be done on the 60th day of pregnancy, when you can see whether the development of the sac, buds and heart is normal or not. If there are fetal buds but no fetal heart, it may be an abnormality.
If no fetal heart is found after repeated checkups, it is important to be alert to the possibility of embryonic failure, which requires prompt medical attention and symptomatic treatment.