We investigated whether enhanced expression of αB crystallin, a stress‐inducible molecular chaperone of the small heat shock family, can protect myocardial contractile apparatus against ischemia reperfusion (I/R) injury. Transgenic mice overexpressing αB crystallin were generated using the 0.76 kb rat αB crystallin cDNA cloned into a pCAGGS plasmid driven by a human cytomegalovirus expression system. Southern analysis confirmed transgene integration and Northern and Western blotting characterized expression (3.1‐fold and 6.9‐fold elevations in myocardial mRNA and protein levels, respectively). Extent of functional recovery overa3hreperfusion period following a 20 min ischemic period in transgenic and wild‐type mouse hearts was assessed using an ex vivo work‐performing heart preparation. The transgenic group displayed significantly higher values of DP at R45 min (29.14±1.9mmHgvs. 17.6±0.7 mm Hg), R60 min (31.56±1.7mmHgvs. 17.8±0.8 mm Hg), and R75 min (32.5±2.2 mm Hg vs. 16.9±0.9 mm Hg), and of dLVP/dt at R45 min (1740.2±111.5 mm Hg.s⁻¹ vs. 548.7±82.2 mm Hg.s⁻¹) and R60 min (1199.8±104.6 mm Hg.s⁻¹ vs. 466.9±61.1 mm Hg.s⁻¹). The transgenic group also displayed development of less oxidative stress, decreased extent of infarction, and attenuated cardiomyocyte apoptotic cell death. Transgene overexpression of αB crystallin was therefore successful in diminishing the independent contributory effects of both necrosis and apoptosis on I/R‐induced cell death.—Ray, P. S., Martin, J. L., Swanson, E. A., Otani, H., Dillmann, W. H., Das, D. K. Transgene overexpression of aB crystallin confers simultaneous protection against cardiomyocyte apoptosis and necrosis during myocardial ischemia and reperfusion. FASEB J. 15, 393‐402 (2001)