Impaired regulation of blood glucose levels in diabetes mellitus (DM) patients and the associated elevation of blood glucose levels are known to increase the risk of diabetic cardiomyopathy (DC). In the present study, a probiotic bacterium, Lactobacillus reuteri GMN-32, was evaluated for its potential to reduce blood glucose levels and to provide protection against DC risks in streptozotocin (STZ)-induced DM rats. The blood glucose levels of the STZ-induced DM rats when treated with L. reuteri GMN-32 decreased from 4480 to 3620 mg/l (with 10⁷ colony-forming units (cfu)/d) and 3040 mg/l (with 10⁹ cfu/d). Probiotic treatment also reduced the changes in the heart caused by the effects of DM. Furthermore, the Fas/Fas-associated protein with death domain pathway-induced caspase 8-mediated apoptosis that was observed in the cardiomyocytes of the STZ-induced DM rats was also found to be controlled in the probiotic-treated rats. The results highlight that L. reuteri GMN-32 treatment reduces blood glucose levels, inhibits caspase 8-mediated apoptosis and promotes cardiac function in DM rats as observed from their ejection fraction and fractional shortening values. In conclusion, the administration of L. reuteri GMN-32 probiotics can regulate blood glucose levels, protect cardiomyocytes and prevent DC in DM rats.