Hjärtasjön-Östersjön and Molången are lakes in faults in the northern part of Tylöskogen's forest area.
The catchment areas for the lakes consist mainly of forest land and the settlements around the lakes are sparse. Large parts of the shore areas around Hjärtasjön are nature reserves (Kopparbergs Äng and Hjärtasjöns Skärgård).
The lakes are home to perch, bream, bream, pike, roach, rudd, sablefish, tench and rudd. American brook trout are found upstream and have also been found in the lake system, as are pike and eel. Boating is possible at Hjärtasjön's western bay.
