The presence of sinus tachycardia in the mother does not necessarily have an effect on the fetus if there is no other heart condition. During pregnancy, the body makes a series of adjustments to accommodate the development of the fetus. In late pregnancy, the heart volume increases by about 10%, the heart rate increases by 10-15 beats per minute at rest, and the cardiac output increases by about 30% compared to that of a non-pregnant woman. Therefore, if a pregnant woman does not have any underlying heart disease, tachycardia during pregnancy generally has no effect on the fetus. However, if a pregnant woman has a heart condition, high blood pressure, or other illnesses such as fever that cause sinus tachycardia, these illnesses can affect the development of the fetus and have an adverse effect on the fetus. Therefore, when sinus tachycardia occurs, you need to check the cause of its appearance, and if it is accompanied by other diseases, you need to seek medical treatment in time.