The leukaemia inhibitory factor is a cytokine that exhibits pleiotropic activities in a wide range of cell types. There are evidences that leukaemia inhibitory factor-regulated signalling pathways are involved in cardiomyogesis and maintenance of cardiomyocytes. In the present work we studied the effect of leukaemia inhibitory factor on cardiomyogenesis of embryonic stem cells together with the role of serum-born factors. We showed that leukaemia inhibitory factor had an inhibitory effect during both the induction and progression phases of cardiomyogenesis of embryonic stem cells. The leukaemia inhibitory factor-mediated inhibition of cardiomyogenesis was abolished by inhibitors of STAT3 activity. These results suggest that leukaemia inhibitory factor- activated STAT3 is responsible for the inhibition of cardiomyogenesis in embryonic stem cells.