No visualisation of fetal heart at this stage could be because of wrong dates or a failing pregnancy. Either ways, this can be sorted out. If the fetal heart is still absent and the sac size is more than 28 mm, it probably means a failed pregnancy, a common enough phenomenon and you should not be so worried. In the first few weeks as many as 22 % or more pregnancies abort and this happens mainly because of an abnormal conception of the fetus. In such a situation, it is always suggested to abort the fetus, as preserving it artificially can result in further complications.
So please get a scan in a weeks time. If the fetal heart is still not seen, just accept the inevitable. By and large, this should have no bearing on your subsequent pregnancies. And if fetal heart is seen, the pregnancy can be continued normally.