Normally a faint fetal heartbeat at 45 days of pregnancy is normal. In the case of 45 days of pregnancy, the fetal heart may not have been detected yet. This is because the germs and the fetal heartbeat are usually visible on ultrasound at 6-7 weeks of pregnancy. If the fetal heart is weak or even undetectable at 45 days of pregnancy, it is possible that the delay in the last menstrual period has resulted in a late implantation of the embryo. Therefore, if the fetal heartbeat is still undetectable or weak on the 45th day of pregnancy, it is recommended to review the pregnancy in 1-2 weeks, and pay attention to whether the pregnant woman has any uncomfortable symptoms. Generally speaking, on the 45th day of pregnancy, the fetal buds have just formed and the embryo is still too small, so the fetal heart may be detected weakly, which is normal, as long as the development of the fetus is normal.