Objective:To investigate the changes of FHL1(Four and a half LIM domains protein 1) gene mRNA and protein expression during the differentiation of P19 cells to cardiac myocytes,and to explore the relationship between FHL1 gene and the differentiation stage of cardiacmyocytes. Methods:P19 cells were cultured with DMSO in suspension for 4 days to form cell aggregation. Then the aggregates were cultured on gelatin-coated culture dishes without DMSO up to 14 days. The beating of cells was observed. Western Blot of Cardiac Troponin I(cTnI) were used to identify cells differentiating into cardiac cells. Total RNA and protein were extracted from P19 cells during the process of differentiation at various time points. The levels of FHL1 mRNA and protein were evaluated by RT-PCR and Western blot,respectively. Results:After induced by DMSO for 4 days in suspension,spontaneous and rhythmically beating cells were seen at 8 day,which were cTnI-positive. When P19 cells were induced to differentiate into cardiac myocytes,both the expression level of FHL1 gene mRNA and protein were up-regulated gradually during 0~8 days of differentiation. The FHL1 gene mRNA and protein expression were obviously up-regulated. There were significant differences among the different days(P < 0.05). From 8 th~14 th day,both the mRNA and protein expression of FHL1 gene were kept in higher level,and there was no significant differences among different days(P > 0.05). Conclusion:Both the expression of FHL1 gene and protein were up-regulated in the process of the differentiation of P19 cells into cardiacmyocytes,which might be involved in the differentiation of cardiac rnyocytes.