Abstract： To examine the effect of simulated weightlessness on inducible HSP70 expression in the heart and vessel tissues of rats, a tail-suspension rat model was used to simulate weightlessness. HSP72 mRNA and HSP70 expression in heart and vessel tissues of both simulated weightless and control rats exposed to heat stress (ambient temperature, Ta=43℃) and recovered at Ta of 25℃ for 1 h (CON-H1, SUS-H1) or 2 h (CON-H2, SUS-H2) were analyzed using Northern blot and Western blot. The expression of HSP72 mRNA in the myocardium significantly decreased in SUS-H2, as compared with that of CON-H2 rats. The amount of HSP72 in the myocardium tended to decrease in both SUS-H1 and SUS-H2 groups, as compared with the corresponding control groups, but the differences were not statistically significant. The levels of inducible HSP70 expression in the vessels were related with their anatomical locations, for that the expression of both HSP72 mRNA and HSP72 significantly increased in basilar arteries, whereas it showed a slight decline in femoral arteries. The blunted HSP70 expression in myocardium suggests that simulated weightlessness may induce myocardial changes similar to those in aging. However, the HSP70 expression changes in arteries are in accord with the trend of differential adaptation changes in vessels to simulated weightlessness.