Previous work has shown that the endogenous cystathionine gamma-synthase (CSE)/hydrogen sulfide (H2S) pathway participates in the regulation of cardiac contraction. We hypothesized that the pathway might participate in the pathophysiological regulation of ischemic heart disease. Isoproterenol injection of rat hearts induced a myocardial ischemic injury model, with reduced myocardial and plasma H2S levels, decreased C-SE activity, and upregulated CSE gene expression. Exogenous administration of the H2S donor NaHS reduced the mortality rate: increased left-ventricular pressure development and left-ventricular-end systolic pressure; and decreased left-ventricular-end diastolic pressure (LVEDP) and subendocardial necrosis, capillary dilatation, leukocytic infiltration, fibroblast swelling, and fibroblastic hyperplasia. As well, production of lipid peroxidation, including myocardial malondialdehyde (MDA), and plasma MDA and Conjugated diene, was reduced. Oxidative stress injury is an important mechanism of isoproterenol-induced myocardial injury. In vitro experiments revealed that NaHS might antagonize myocyte MDA production by oxygen-free radicals and that NaHS directly scavenged hydrogen peroxide and superoxide anions. Our results suggest that the endogenous CSE/H2S pathway contributes to the pathogenesis of isoprotereriol-induccd myocardial injury. Administration of exogenous H2S effectively protects myocytes and contractile activity, at least by its direct scavenging of oxygen-free radicals and reducing the accumulation of lipid peroxidations. (C) 2004 Elsevier Inc. All rights reserved.