Oxidant stress-induced activation of poly(ADP-ribose) polymerase (PARP) plays a role in the pathogenesis of various cardiovascular diseases. We have now investigated the role of PARP in the process of cardiac remodeling and heart failure in a mouse model of heart failure induced by transverse aortic constriction (banding). The catalytic activity of PARP was inhibited by the potent isoindolinone-based PARP inhibitor INO-1001 or by PARP-1 genetic deficiency. PARP inhibition prevented the pressure overload-induced decrease in cardiac contractile function, despite the pressure gradient between both carotid arteries being comparable in the two experimental groups. The development of hypertrophy, the formation of collagen in the hearts, and the mitochondrial-to-nuclear translocation of the cell death factor apoptosis-inducing factor (AIF) were attenuated by PARP inhibition. The ability of the inhibitor to block the catalytic activity of PARP was confirmed by immunohistochemical detection of poly(ADP-ribose), the product of the enzyme in the heart. Plasma levels of INO-1001, as measured at the end of the experiments, were in the concentration range sufficient to block the oxidant-mediated activation of PARP in murine cardiac myocytes in vitro. Myocardial hypertrophy and AIF translocation was also reduced in PARP-1-deficient mice undergoing aortic banding, compared with their wild-type counterparts. Overall, the current results demonstrate the importance of poly(ADP-ribos)ylation in the pathogenesis of banding-induced heart failure.Poly(ADP-ribose) polymerase (PARP)-1, a monomeric enzyme present in eukaryotes, is the major isoform of an expanding family of poly(ADP-ribosyl)ating enzymes (for review, see Virá g and Szabó, 2002). The main isoform of the family, PARP-1, primarily functions as a DNA damage sensor in the nucleus. Upon binding to damaged DNA mainly through the second zinc finger domain, PARP-1 forms homodimers and catalyzes the cleavage of NAD ϩ into nicotinamide and ADP-ribose and uses the latter to synthesize branched nucleic acid-like polymers poly(ADP-ribose) covalently attached to nuclear acceptor proteins. The biological role of PARP-1 is complex and includes the regulation of DNA repair and maintenance of genomic integrity.PARP-1 has been implicated in a variety of pathophysiological processes. PARP is an energy-consuming enzyme, which transfers ADP ribose units to nuclear proteins. As a result of this process, the intracellular nicotinamide dinucleotide (oxidized) (NAD ϩ ) and ATP levels remarkably decrease, resulting in cell dysfunction and cell death via the necrotic route (for review, see Virá g and Szabó, 2002).PARP becomes activated in response to DNA single-strand breaks, which can develop as a response to free radical and oxidant cell injury. Oxidative and nitrosative stress triggers the activation of the nuclear enzyme PARP, which contributes to the pathogenesis of various cardiovascular diseases, including myocardial infarction and ischemia-reperfusion and heart failure (for review, s...