To investigate the changes of the metabolism of rat myocardiac cells cultured in vitro under simulated weightlessness and gamma-irradiation, rat myocardiac cells were rotated on a horizontal clinostat, and irradiated with 2Gy 60Co gamma-ray. The results showed: (1) after irradiation, the LDH activity and SOD concentrations showed a significant increase, and the MDA concentration also increased. (2) After irradiation, LDH activity increased 60% on the 3rd day, and SOD concentration almost doubled on the first day. (2) MDA concentration also increased but it reduced to normal after the 3rd day. (3) Simple rotation on the clinostat showed no effect on the parameter, but there was a synergistic effect when it was combined with gamma-irradiation.