The best time for fetal heart ultrasound is between 24-28 weeks of gestation, when the fetal heart is basically well developed, the amniotic fluid volume is relatively high, the fetus has more room to move around in the uterus, and the fetal position is more suitable for observing the heart. Fetal heart ultrasound can check for congenital heart disease, including ventricular septal defect, atrial septal defect, tetralogy of Fallot, etc. If a relatively minor heart development abnormality is found, such as ductus arteriosus, it may be related to the young gestational age of the fetus and the heart is not yet well developed. If the ultrasound reveals abnormal fetal heart development, prenatal diagnosis such as amniocentesis or umbilical cord blood sampling should be performed to rule out fetal chromosomal abnormalities. In cases of chromosomal abnormalities, the fetus may be born with a variety of fetal malformations, which are not always viable and usually require timely termination of pregnancy.