Diagnostics of the masses belongs to the frequent indications of echocardiography. The interpretation is not always simple and it requires besides the experience a very good knowledge of intra- and extracardiac anatomy too. The echocardiographer has to master thoroughly normal structures and their variants that may mimic the pathologic conditions. The first part of an educative article deals with the overview of masses and pseudomasses of the left atrium. Our experience with differential diagnostics of them is presented. The article is focused on image documentation.