1.Assessment of normal fetal cardiac function: the characteristics of fetal cardiac function: tricuspid flow velocity and pulmonary artery flow velocity during diastole are higher than mitral valve and aorta, and the acceleration time of right ventricular ejection is shorter than the corresponding time of left ventricle, indicating the predominance of fetal right ventricular function; fetal ventricular diastolic function is lower than that of normal children; fetal pulmonary circulation resistance is higher than that of body circulation resistance, etc. 2.Diagnosis of fetal congenital heart disease: The application of two-dimensional and Doppler ultrasound techniques can sensitively detect the presence of structural and blood flow abnormalities, regurgitation and shunt lesions in the fetal heart, and make quantitative analysis of the extent of lesions. 3.Analysis of heart rate arrhythmias: The use of Doppler ultrasound technology can diagnose atrial premature beats, ventricular premature beats, atrioventricular block and other heart rate arrhythmias.