RESUMO
To understand the physiological effects of substances used in drugs and therapies on heart muscle tissue, model systems that mirror the in vivo situation of living tissues are required. Therefore, the creation of 3-dimensional (3D) cell aggregates provides an improved and refined in vitro model as a link between cell-free or single cells and organs or whole organisms in vivo. Here we have characterized a stable contracting in vitro tissue model, which consists of embryonic chicken cardiomyocytes. For establishing a cell-based test system, the 3D in vitro cardiomyocyte spheres were characterized according to messenger RNA expression of special cardiac cell types and protein expression pattern of functional markers such as connexin-43. Finally, the in vitro spheroid model was used for investigating the effect of isoproterenol, a *-adrenergic receptor agonist, on the contractibility mediated by the ligand receptor interaction.