Hello, and I hope I can help you today. Many women experience a fast heartbeat while they are pregnant, and as long as the doctors evaluation of her heart as well is for other medical problems the can cause rapid heartbeat, such as thyroid disease, are negative than the symptom is likely just due to pregnancy. A pregnant woman s blood volume increases to one half times greater capacity during pregnancy to provide the placenta with oxygen as well is prepare her body for childbirth, so during the adjustment period, her body may just be under some additional stress. Furthermore, if your wife has gained a lot of weight since the beginning of the pregnancy, even ordinary activities can make her heart race compared to when she is not pregnant. So in summary, as long as your wife is under proper medical care and receiving an evaluation, there really is no reason to worry. Furthermore, your wife s rapid heartbeat does not have any negative effect on the fetus so there is no need to worry about the baby in the situation. I hope that I was adequately able to answer your question today, and that my advice was helpful. Best wishes, Dr. Brown