The steroid hormone 1,25(OH)(2)-vitamin D(3) [1,25D] has been shown to affect the growth and proliferation of primary cultures of ventricular myocytes isolated from neonatal rat hearts. The research presented here shows that the vitamin D receptor [VDR] is present in murine cardiac myocytes (HL-1 cells), and that 1,25D affects the growth, proliferation and morphology of these cells. In addition we show that 1,25D effects expression of ANP, myotrophin, and c-myc. Furthermore, 1,25D effects expression and localization of the VDR within the cell. Murine HL-1 cardiac myocytes were grown and treated with 1,25D in culture, and growth and morphology were assessed with microscopic analysis. Cells were counted and protein levels were evaluated through Western blot analysis. Subcellular localization of the VDR was determined using immunofluorescence and confocal microscopy. 1,25D was found to decrease proliferation and alter cellular morphology of the HL-1 cells. Treatment with 1,25D increased expression of myotrophin while decreasing expression of atrial natriuretic peptide [ANP] and c-myc. 1,25D treatment also increased expression and nuclear localization of the VDR in these cardiac myocytes. Thus 1,25D is an important hormone involved in modulating and maintaining heart cell structure and function.