['Previous studies have demonstrated that ischemic preconditioning prevents lethal cell injury and, as a consequence, limits infarct size in rat heart. Although both apoptosis and necrosis have been shown to contribute to myocardial cell death after myocardial ischemia and reperfusion, the ability of ischemic preconditioning to prevent programmed cell death remains unknown.', 'To test the hypothesis that ischemic preconditioning reduces irreversible ischemic injury in part by decreasing apoptosis, rats that underwent ischemic preconditioning and controls were subjected to 30 minutes of left coronary artery occlusion followed by 180 minutes of reperfusion. Ischemic preconditioning was achieved by five 5-minute cycles of ischemia, each followed by 5 minutes of reperfusion. Infarct size, determined by dual staining with triphenyltetrazolium chloride and phthalocyanine blue dye, was significantly reduced in preconditioned compared with nonpreconditioned rats (11.4+/-1.4% versus 58.7+/-1.4%; n=20 in each group; P<.001; infarct size/risk area). Genomic DNA from preconditioned hearts showed little or no oligonucleosome-sized fragments (200-bp multiples), whereas genomic DNA from nonpreconditioned hearts showed a typical nucleosome fragmentation. The TUNEL assay localized fewer and sparsely stained nuclei within the infarct zone of ischemic preconditioned hearts compared with nonpreconditioned hearts. Consistent with these findings, the number of cytosolic histone-associated low-molecular-weight DNA fragments was significantly decreased in preconditioned hearts compared with controls (0.17+/-0.02 versus 1.07+/-0.09 U; n=10 in each group; P<.001; absorbance 405 nm/490 nm).'] Does ischemic preconditioning decrease apoptosis in rat hearts in vivo?