Postconditioning prevents cardiomyocytes from ischemia/reperfusion-induced apoptosis. However, little is known about the molecular mechanisms that mediate the cardioprotective effect of postconditioning. Here, we hypothesized that postconditioning targeted p53 upregulated modulator of apoptosis (PUMA) to protect cardiomyocytes against endoplasmic reticulum stress-mediated apoptosis. Our results demonstrated that postconditioning could inhibit GRP78 (78-kDa glucose-regulated protein) expression, caspase-12 activation, and cardiomyocyte apoptosis by regulating PUMA expression. In addition, p53 is involved in the regulatory role of postconditioning in PUMA expression. Our data reveal a cardioprotective pathway of postconditioning in which it represses PUMA.