Hello, I understand your concern. This kind of uncertainty while expecting can be a torture. However, a shadow on a fetal heart on the ultrasound is common. It is usually due to calcium deposits on the heart which often turn out to be nothing. But, nonetheless, it can be an indicator to an underlying pathology. It can either be a heart defect or a marker for Down Syndrome. By this time, I m sure you have undergone the necessary tests and blood work in order to exclude Down Syndrome, so if the test are negative, this possibility can be excluded with a certain degree of confidence. The second ultrasound will clarify everything. In the mean time, it is the sensible thing to do not to worry too much, because, first, it might turn out to be nothing, second, mother s stress is not a healthy thing for both of you. A positive attitude can get you through anything in life. Wishing you a happy and healthy pregnancy and all the best.