Infarcted areas of rabbit myocardium show relatively higher inducible nitric oxide synthase activity, measured by the conversion of L-[14C]arginine to L-[14C]citrulline. The principal finding in this study is that dexamethasone (2 mg/kg) prevents the induction of inducible nitric oxide synthase in heart muscle when given before, or even 3 hr after coronary artery ligation. Additionally cyclic GMP levels remain unchanged following treatment with dexamethasone. It is possible that the enhanced production of nitric oxide by inducible nitric oxide synthase accounts, at least in part, for the depression of myocardial contractility seen in myocardial infarction and in other clinical conditions.