Abstract: Objective To investigate the role of tunicamyocin(TM) in inducing apoptosis of cardiac muscle cells in rats and the possible apoptosis pathway. Methods Primary cardiac muscle cells were isolated from neonatal rats with the modified 2- step collagenase digest method. Apoptosis of these cells, induced by TM at an appropriate concentration and incubated for a certain time, was detected by MTT assay, DNA ladder and Hoechst staining. Expression of Grp78 and procaspase-12 in the process of apoptosis was detected by Western blot. Results Apoptosis with typical morphologic changes occurred in 30% of cardiac muscle cells 24 hours after induction with TM at the concentration of 5μg/mL.The expression of Grp78 and caspase-12 and diffuse changes in DNA smear could be detected 3, 24, and 48h, respectively, after induction with TM. Conclusion Apoptosis of primary cardiac muscle cells in rats can be induced by TM through the endoplasmic reticulum stress-associated pathway, 5μg/mL TM and 24-hour incubation may be the proper conditions for establishing an apoptosis model.