As others have said, the Orthodox approach is not to categorise sin as "mortal" and "venial":
A very wise priest once said to me: All sins are stains on our souls. A handkerchief is either clean, or it is not. It may have only been used once, but it is still soiled, no matter if only by a speck. If the President, Prime Minister, or the King or Queen suddenly needed a handkerchief, and you were the only one close enough who had one, if you knew it was unclean, even if only slightly, would you give it to him/her?
Food for thought.