Fetal intracardiac strong echogenic dots are ultrasound phenomena that appear in the fetal ventricle with echoes similar to or stronger than the adjacent femoral echoes. They usually appear as strong echogenic foci in the tendon or mastoid muscle and move in synchrony with the heart beat cycle. The location of fetal intracardiac strong echogenic foci is usually found in the left ventricle, but can also be found in the right ventricle, or in both the left and right ventricles. The detection rate is influenced by the quality and resolution of the instrument, the skill and experience of the examiner, the position of the fetus, the condition of the pregnant woman, and the gestational age. The detection rate in the population ranges from 0.13% to 20%, with a mean of 4.5%. Asian populations have higher detection rates than other ethnic groups. It has been found that 2% of chromosomally normal fetuses have these changes, which may be normal variants of the mastoid muscle or microcalcifications of the mastoid muscle; 15% of chromosomally abnormal fetuses have these changes, which may be due to ischemic changes in the mastoid muscle caused by abnormal development of the coronary artery terminal microtubule system.