If i started having brown discharge 3 days ago, us showed no heart beat today on 7weeks pg. is natural miscarriage likely to begin soon?

Yes: Generally the spotting is the first sign of a miscarriage. Some women are such good moms that their bodies hold on to the baby and they have what is known as a missed abortion ( all early losses are called abortions) and have to have a D&C. Hope this helps. Remember this isn't because of anything you did or didn't do and does not increase the risk of it happening again.