OBJECTIVE We investigated whether vesnarinone alters the induction of nitric oxide (NO) synthesis by bacterial lipopolysaccharide (LPS) or in combination with interferon-gamma in cultured J774 macrophages and rat cardiac myocytes. METHODS The induction of NO synthesis was determined by measuring the stable end-product nitrite. The cytotoxic effect of vesnarinone was assessed by measuring cell respiration. Any change in mRNA levels for NO synthase (NOS) was determined by RT-PCR. RESULTS Stimulation by LPS or in combination with interferon-gamma increased the accumulation of nitrite in the supernatant of J774 macrophages or cardiac myocytes. NOS induction accounted for this accumulation of nitrite, as dexamethasone, NG-methyl-L-arginine, and cycloheximide each reduced the production of nitrite in both types of cells. Vesnarinone produced a significant decline in the cumulative production of nitrite in both types of cells without evidence of cytotoxicity. However, the addition of vesnarinone after induction of NOS did not inhibit nitrite production. Treatment with LPS or in combination with interferon-gamma led to a significant expression of NOS mRNA in both types of cells that was significantly reduced by vesnarinone. CONCLUSIONS Vesnarinone inhibited NO synthesis by inhibiting the induction of NOS in J774 macrophages and cardiac myocytes. This drug may exert a beneficial effect in patients with heart failure, in part, by attenuating the production of NO.