Objective: To investigate the effects of Tongxinluo (TXL) on hypertrophy of H9c2 cardiomyocytes and connexin 43 mRNA expression induced by isoproterenol (Iso). Method: Cultured H9c2 cardiomyocytes were randomly divided into four groups: control group

TXL group

Iso group

and Iso+TXL group. After 72 hours of culture

cell size was determined by phase contrast microscope

the protein concentrations were measured by BCA method and the expression of Cx43 mRNA were measured by reverse transcription polymerase chain reaction (RT-PCR). Result: Cell size of H9c2 cardiomyocytes of the Iso group (P<0.05) was increased more prominently than the control group. Compared with Iso group

Tongxinluo attenuated the increase of cardiomyocytes size (P<0.05). H9c2 cardiomyocytes protein concentrations in the Iso group (P<0.05) was increased more significantly than the control group. Although Tongxinluo didn't affect the normal H9c2 cardiomyocytes protein concentration

it inhibited the increase of protein concentrations induced by Iso (P<0.05).Iso decreased Cx43 mRNA expression of H9c2 cardiomyocytes more evidently than that of the control group (P<0.05)

which was inhibited by Tongxinluo (P<0.05). Conclusion: Tongxinluo can prevent the hypertrophy of H9c2 cardiomyocytes and down-regulate of Cx43 mRNA expression induced by Iso.