A reduction in the risk of coronary heart disease has been associated to moderate red wine consumption. We tested whether a nonalcoholic red wine extract would open mitochondrial K(ATP) channels in guinea pig myocytes. The opening of mitochondrial K(ATP) channels was assessed by endogenous flavoprotein fluorescence. Red wine extract (100 μg·mL(-1)) increased flavoprotein oxidation (10.9% ± 1.2%, n = 20). This effect was prevented by the mitochondrial K(ATP) channel blocker, 5-hydroxydecanoate (500 µmol·L(-1); 0.3% ± 1.1%, n = 13), confirming the hypothesis that red wine extract opens mitochondrial K(ATP) channels.