Aim: To explore whether overexpression of the small heat shock protein HSP20 in rat cardiomyocytes protects against simulated ischemia/reperfusion (SI/R) injury. Methods: Recombinant adenovirus expressing HSP20 was used to infect rat H9c2 cardiomyocytes at high efficiency, as assessed by green fluorescent protein. H9c2 cells were subjected to SI/R stress; survival was estimated through assessment of lactate dehydrogenase and cell apoptosis through caspase-3 activity. Results: Overexpression of HSP20 decreased lactate dehydrogenase release by 21.5% and caspase-3 activity by 58.8%. Pretreatment with the protein kinase C inhibitor Ro-31-8220 (0.1 mu mol/L) for 30 min before SI/R canceled the protective effect of HSP20. The selective mitochondrial K-ATP(+), channel inhibitor 5-hydroxydecanoate (100 mu mol/L) had a similar effect. However, the non-selective K-ATP(+), channel inhibitor glibenclamide (100 mu mol/L) had no significant effect. Conclusion: These data indicate that the protective effect of HSP20 in vitro is primarily due to reduced necrotic and apoptotic death of cardiomyocytes, possibly via the protein kinase C/mitochondrial K(+)ATP pathway.