My LO had it [It's called an EIF - Echogenic Intracardiac Focus] and it scared the life out of dh and I when they found it as I hadn't a clue what it was or what it meant and they didn't help by giving much info.... It was still there at the follow up but my LO is now 5 months old and it has had zero affect on her heart or health.
It's fairly common and unless they see other indications of abnormalities, it's usually completely harmless [although they sure like to scare you when you get the news, made me mad that they had us worried sick for so long.] I really really hope that either way, even if it's still there on your scan tomorrow that it doesn't bring any other issues.
This is from the Wiki page:
Echogenic intracardiac focus (EIF) is a small bright spot seen in the babys heart on an ultrasound exam. This is thought to represent mineralization, or small deposits of calcium, in the muscle of the heart. EIFs are found in about 3-5% of normal pregnancies and cause no health problems.
EIFs themselves have no impact on health or heart function. Often the EIF is gone by the third trimester. If there are no problems or chromosome abnormalities, EIFs are considered normal changes, or variants.
Hope this helps to ease your fear a bit