I believe the is Bulgarian, and is of Michael Alexander and his son Michael Asen. Not sure if it's a coin though, my thinking is that it's a seal. Is is made of bronze or lead? The missing piece on the edge is too uniform to be a natural break, it could be where the seal was attached to a document.
echizento, thank you very much for answer. I will look further about Bulgarian coins to find out more... if it is coin. It is bronze, very lite and fragile, it has green patina, 0.4g and 17mm diameter.
I think this is it, Bulgarina coin, Ivan Alexander and his son Mikhail. (1331 - 1355). Copper coin. Obv: Alexander and Mikhail, crowned, standing facing. Long-shafted standard between them. Rev: Monogram