Differentiation of human bone marrow mesenchymal stem cells (hBMSC) into the cardiac lineage has been assayed using different approaches such as coculture with cardiac or embryonic cells, treatment with factors, or by seeding cells in organotypic cultures. In most cases, differentiation was evaluated in terms of expression of cardiac-specific markers at protein or molecular level, electrophysiological properties, and formation of sarcomers in differentiated cells. As observed in embryonic stem cells and cardiac progenitors, differentiation of MSC towards the cardiac lineage was preceded by translocation of NKX2.5 and GATA4 transcription factors to the nucleus. Here, we induce differentiation of hBMSC towards the cardiac lineage using coculture with neonatal rat cardiomyocytes. Although important ultrastructural changes occurred during the course of differentiation, sarcomerogenesis was not fully achieved even after long periods of time. Nevertheless, we show that the main cardiac markers, NKX2.5 and GATA4, translocate to the nucleus in a process characteristic of cardiac specification.