This study investigates the protective effects of overexpressing the rat inducible 70-kD heat shock protein (hsp70i) in the heart of transgenic mice against ischemic injury. Transgenic mice were generated with a cytomegalovirus enhancer and β-actin promoter driving hsp70i expression. Unstressed transgene-positive mice showed higher levels of myocardial hsp70i compared to transgene-negative mice after whole-body heat stress, without apparent detrimental effects. Langendorff perfused hearts from transgene-positive and transgene-negative mice were subjected to 20 minutes of warm ischemia and up to 120 minutes of reflow. Results showed that transgene-positive hearts had a 40% reduction in infarct size, doubled contractile function at 30 minutes of reflow, and a 50% reduction in creatine kinase efflux. These findings suggest that increased myocardial hsp70i expression confers protection against ischemic injury, providing potential therapeutic relevance.This study investigates the protective effects of overexpressing the rat inducible 70-kD heat shock protein (hsp70i) in the heart of transgenic mice against ischemic injury. Transgenic mice were generated with a cytomegalovirus enhancer and β-actin promoter driving hsp70i expression. Unstressed transgene-positive mice showed higher levels of myocardial hsp70i compared to transgene-negative mice after whole-body heat stress, without apparent detrimental effects. Langendorff perfused hearts from transgene-positive and transgene-negative mice were subjected to 20 minutes of warm ischemia and up to 120 minutes of reflow. Results showed that transgene-positive hearts had a 40% reduction in infarct size, doubled contractile function at 30 minutes of reflow, and a 50% reduction in creatine kinase efflux. These findings suggest that increased myocardial hsp70i expression confers protection against ischemic injury, providing potential therapeutic relevance.