Transforming growth factor b 1 (TGFb 1 ) has been purported to protect tissues from ischemia-reperfusion (I-R) injury. This study was designed to examine if overexpression of TGFb 1 using adeno-associated virus type 2 (AAV) protects cardiomyocytes from reoxygenation injury. TGFb 1 was overexpressed in cultured HL-1 mouse cardiomyocytes by transfection with AAV/TGFb 1 Latent or with AAV/TGFb 1 ACT (active TGFb 1 ). TGFb 1 upregulation reduced cardiomyocyte apoptosis and necrosis induced by 24 h of hypoxia followed by 3 h of reoxygenation concomitant with reduction in reactive oxygen species release, activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and NFkB expression. Transfection with AAV/TGFb 1 ACT was superior to that with AAV/TGFb 1 Latent . To determine if AAV/TGFb 1 ACT upregulation in vivo would induce cardioprotection from I-R injury, rat hearts were injected with AAV/TGFb 1 ACT or phosphate-buffered saline (PBS). Six weeks later, TGFb 1 ACT was upregulated throughout the myocardium. Following I-R, AAV/TGFb 1 ACT -overexpressing rats had much smaller infarct size (Po0.01 vs PBS group), which was also related to reduced activation of NADPH oxidase and NF-kB, and lower levels of malondialdehyde in I-R tissues. These data demonstrate that overexpression of TGFb 1 by AAV can protect cardiac tissues from reperfusion injury, possibly via antioxidant mechanism. These findings suggest potential of TGFb 1 ACT gene therapy for cardioprotection from I-R injury.