Fetal heart ultrasound cannot usually be done with the fetus lying on its back and it is recommended to wait for the fetus to change its position before examining it. Fetal heart ultrasound is an important test during pregnancy that can effectively rule out the presence of malformations in the fetal heart region. Fetal heart ultrasound requires the fetus to remain in a flat position during the examination, avoiding lying on the stomach or reclining, which will affect the results of the examination and will not be able to accurately understand the development of the fetal heart. If the fetus is not properly positioned in the uterine cavity, the examination will not show clearly, and it is necessary for the pregnant woman to carry out appropriate activities, such as getting out of bed and walking around, turning over from side to side, eating appropriately, rubbing and patting the stomach and other actions, which will prompt the fetus to change its position in the uterus, and then go to the examination again. In addition, fetal heart ultrasound sometimes needs to be repeated several times to complete, and it is also common that the examination is unsuccessful at one time.